description: The numbers 1,   2,   ...,   n ⋅ k are colored with n colors. These colors are indexed by 1,   2,   ...,   n. For each 1 ≤ i ≤ n, there are exactly k numbers colored with color i.
  
  Let [a,   b] denote the interval of integers between a and b inclusive, that is, the set \\{a,   a + 1,   ...,   b\}. You must choose n intervals [a_1,   b_1],   [a_2,   b_2],   ..., [a_n,   b_n] such that: 
  
    * for each 1 ≤ i ≤ n, it holds 1 ≤ a_i < b_i ≤ n ⋅ k; 
    * for each 1 ≤ i ≤ n, the numbers a_i and b_i are colored with color i; 
    * each number 1 ≤ x ≤ n ⋅ k belongs to at most \left⌈ (n)/(k - 1) \right⌉ intervals. 
  
  
  
  One can show that such a family of intervals always exists under the given constraints.
  
  Input
  
  The first line contains two integers n and k (1 ≤ n ≤ 100, 2 ≤ k ≤ 100) — the number of colors and the number of occurrences of each color.
  
  The second line contains n ⋅ k integers c_1,   c_2,   ...,   c_{nk} (1 ≤ c_j ≤ n), where c_j is the color of number j. It is guaranteed that, for each 1 ≤ i ≤ n, it holds c_j = i for exactly k distinct indices j.
  
  Output
  
  Output n lines. The i-th line should contain the two integers a_i and b_i.
  
  If there are multiple valid choices of the intervals, output any.
  
  Examples
  
  Input
  
  
  4 3
  2 4 3 1 1 4 2 3 2 1 3 4
  
  
  Output
  
  
  4 5
  1 7
  8 11
  6 12
  
  Input
  
  
  1 2
  1 1
  
  
  Output
  
  
  1 2
  
  
  Input
  
  
  3 3
  3 1 2 3 2 1 2 1 3
  
  
  Output
  
  
  6 8
  3 7
  1 4
  
  Input
  
  
  2 3
  2 1 1 1 2 2
  
  
  Output
  
  
  2 3
  5 6
  
  Note
  
  In the first sample, each number can be contained in at most \left⌈ (4)/(3 - 1) \right⌉ = 2 intervals. The output is described by the following picture:
  
  <image>
  
  In the second sample, the only interval to be chosen is forced to be [1,   2], and each number is indeed contained in at most \left⌈ (1)/(2 - 1) \right⌉ = 1 interval.
  
  In the third sample, each number can be contained in at most \left⌈ (3)/(3 - 1) \right⌉ = 2 intervals. The output is described by the following picture:
  
  <image>
solution: public class Main {
  
  	public static void main(String[] args) {
  		new Main();
  	}
  
  	public Main() {
  		FastScanner fs = new FastScanner();
  		java.io.PrintWriter out = new java.io.PrintWriter(System.out);
  		solve(fs, out);
  		out.flush();
  	}
  
  	public void solve(FastScanner fs, java.io.PrintWriter out) {
  		int n = fs.nextInt(), k = fs.nextInt();
  		int[] c = new int[n * k];
  		for (int i = 0;i < c.length;++ i) c[i] = fs.nextInt();
  		int[] a = new int[n], b = new int[n];
  		int[] interval = new int[c.length];
  		for (int i = 0;i < c.length;++ i) {
  			int num = c[i] - 1;
  			if (b[num] > 0) continue;
  			if (b[num] == 0) {
  				a[num] = i;
  				b[num] = -1;
  			} else {
  				if (interval[a[num]] > (n - 1) / (k - 1)) {
  					a[num] = i;
  				} else {
  					b[num] = i;
  					for (int j = 0;j < i;++ j) ++ interval[j];
  				}
  			}
  		}
  		for (int i = 0;i < n;++ i) out.println(a[i] + 1 + " " + (b[i] + 1));
  	}
  
  	final int MOD = 998_244_353;
  	int plus(int n, int m) {
  		int sum = n + m;
  		if (sum >= MOD) sum -= MOD;
  		return sum;
  	}
  	int minus(int n, int m) {
  		int sum = n - m;
  		if (sum < 0) sum += MOD;
  		return sum;
  	}
  	int times(int n, int m) {
  		return (int)((long)n * m % MOD);
  	}
  	int divide(int n, int m) {
  		return times(n, IntMath.pow(m, MOD - 2, MOD));
  	}
  	int[] fact, invf;
  	void calc(int len) {
  		len += 2;
  		fact = new int[len];
  		invf = new int[len];
  		fact[0] = fact[1] = invf[0] = invf[1] = 1;
  		for (int i = 2;i < fact.length;++ i) fact[i] = times(fact[i - 1], i);
  		invf[len - 1] = divide(1, fact[len - 1]);
  		for (int i = len - 1;i > 1;-- i) invf[i - 1] = times(i, invf[i]);
  	}
  	int comb(int n, int m) {
  		if (n < m) return 0;
  		return times(fact[n], times(invf[n - m], invf[m]));
  	}
  }
  
  class FastScanner {
  
  	private final java.io.InputStream in = System.in;
  	private final byte[] buffer = new byte[8192];
  	private int ptr = 0;
  	private int buflen = 0;
  
  	private boolean hasNextByte() {
  		if (ptr < buflen) return true;
  		ptr = 0;
  		try {
  			buflen = in.read(buffer);
  		} catch (java.io.IOException e) {
  			e.printStackTrace();
  		}
  		return buflen > 0;
  	}
  
  	private byte readByte() {
  		return hasNextByte() ? buffer[ptr++ ] : -1;
  	}
  
  	private static boolean isPrintableChar(byte c) {
  		return 32 < c || c < 0;
  	}
  
  	private static boolean isNumber(int c) {
  		return '0' <= c && c <= '9';
  	}
  
  	public boolean hasNext() {
  		while (hasNextByte() && !isPrintableChar(buffer[ptr]))
  			ptr++ ;
  		return hasNextByte();
  	}
  
  	public String next() {
  		if (!hasNext()) throw new java.util.NoSuchElementException();
  		StringBuilder sb = new StringBuilder();
  		byte b;
  		while (isPrintableChar(b = readByte()))
  			sb.appendCodePoint(b);
  		return sb.toString();
  	}
  
  	public final char nextChar() {
  		if (!hasNext()) throw new java.util.NoSuchElementException();
  		return (char)readByte();
  	}
  
  	public final long nextLong() {
  		if (!hasNext()) throw new java.util.NoSuchElementException();
  		long n = 0;
  		try {
  			byte b = readByte();
  			if (b == '-') {
  				while (isNumber(b = readByte()))
  					n = n * 10 + '0' - b;
  				return n;
  			} else if (!isNumber(b)) throw new NumberFormatException();
  			do
  				n = n * 10 + b - '0';
  			while (isNumber(b = readByte()));
  		} catch (java.util.NoSuchElementException e) {}
  		return n;
  	}
  
  	public final int nextInt() {
  		if (!hasNext()) throw new java.util.NoSuchElementException();
  		int n = 0;
  		try {
  			byte b = readByte();
  			if (b == '-') {
  				while (isNumber(b = readByte()))
  					n = n * 10 + '0' - b;
  				return n;
  			} else if (!isNumber(b)) throw new NumberFormatException();
  			do
  				n = n * 10 + b - '0';
  			while (isNumber(b = readByte()));
  		} catch (java.util.NoSuchElementException e) {}
  		return n;
  	}
  
  	public double nextDouble() {
  		return Double.parseDouble(next());
  	}
  }
  
  class Arrays {
  
  	public static void sort(final int[] array) {
  		sort(array, 0, array.length);
  	}
  
  	public static void sort(final int[] array, int fromIndex, int toIndex) {
  		if (toIndex - fromIndex  <= 512) {
  			java.util.Arrays.sort(array, fromIndex, toIndex);
  			return;
  		}
  		sort(array, fromIndex, toIndex, 0, new int[array.length]);
  	}
  
  	private static final void sort(int[] a, final int from, final int to, final int l, final int[] bucket) {
  		if (to - from  <= 512) {
  			java.util.Arrays.sort(a, from, to);
  			return;
  		}
  		final int BUCKET_SIZE = 256;
  		final int INT_RECURSION = 4;
  		final int MASK = 0xff;
  		final int shift = l << 3;
  		final int[] cnt = new int[BUCKET_SIZE + 1];
  		final int[] put = new int[BUCKET_SIZE];
  		for (int i = from; i < to; i++) ++ cnt[(a[i] >>> shift & MASK) + 1];
  		for (int i = 0; i < BUCKET_SIZE; i++) cnt[i + 1] += cnt[i];
  		for (int i = from; i < to; i++) {
  			int bi = a[i] >>> shift & MASK;
  			bucket[cnt[bi] + put[bi]++] = a[i];
  		}
  		for (int i = BUCKET_SIZE - 1, idx = from; i >= 0; i--) {
  			int begin = cnt[i];
  			int len = cnt[i + 1] - begin;
  			System.arraycopy(bucket, begin, a, idx, len);
  			idx += len;
  	    }
  		final int nxtL = l + 1;
  		if (nxtL < INT_RECURSION) {
  			sort(a, from, to, nxtL, bucket);
  			if (l == 0) {
  				int lft, rgt;
  				lft = from - 1; rgt = to;
  				while (rgt - lft > 1) {
  					int mid = lft + rgt >> 1;
  					if (a[mid] < 0) lft = mid;
  					else rgt = mid;
  				}
  				reverse(a, from, rgt);
  				reverse(a, rgt, to);
  	        }
  	    }
  	}
  
  	public static void sort(final long[] array) {
  		sort(array, 0, array.length);
  	}
  
  	public static void sort(final long[] array, int fromIndex, int toIndex) {
  		if (toIndex - fromIndex  <= 512) {
  			java.util.Arrays.sort(array, fromIndex, toIndex);
  			return;
  		}
  		sort(array, fromIndex, toIndex, 0, new long[array.length]);
  	}
  
  	private static final void sort(long[] a, final int from, final int to, final int l, final long[] bucket) {
  		final int BUCKET_SIZE = 256;
  		final int LONG_RECURSION = 8;
  		final int MASK = 0xff;
  		final int shift = l << 3;
  		final int[] cnt = new int[BUCKET_SIZE + 1];
  		final int[] put = new int[BUCKET_SIZE];
  		for (int i = from; i < to; i++) ++ cnt[(int) ((a[i] >>> shift & MASK) + 1)];
  		for (int i = 0; i < BUCKET_SIZE; i++) cnt[i + 1] += cnt[i];
  		for (int i = from; i < to; i++) {
  			int bi = (int) (a[i] >>> shift & MASK);
  			bucket[cnt[bi] + put[bi]++] = a[i];
  		}
  		for (int i = BUCKET_SIZE - 1, idx = from; i >= 0; i--) {
  			int begin = cnt[i];
  			int len = cnt[i + 1] - begin;
  			System.arraycopy(bucket, begin, a, idx, len);
  			idx += len;
  	    }
  		final int nxtL = l + 1;
  		if (nxtL < LONG_RECURSION) {
  			sort(a, from, to, nxtL, bucket);
  			if (l == 0) {
  				int lft, rgt;
  				lft = from - 1; rgt = to;
  				while (rgt - lft > 1) {
  					int mid = lft + rgt >> 1;
  					if (a[mid] < 0) lft = mid;
  					else rgt = mid;
  				}
  				reverse(a, from, rgt);
  				reverse(a, rgt, to);
  	        }
  	    }
  	}
  
  	public static void reverse(int[] array) {
  		reverse(array, 0, array.length);
  	}
  
  	public static void reverse(int[] array, int fromIndex, int toIndex) {
  		for (-- toIndex;fromIndex < toIndex;++ fromIndex, -- toIndex) {
  			int swap = array[fromIndex];
  			array[fromIndex] = array[toIndex];
  			array[toIndex] = swap;
  		}
  	}
  
  	public static void reverse(long[] array) {
  		reverse(array, 0, array.length);
  	}
  
  	public static void reverse(long[] array, int fromIndex, int toIndex) {
  		for (-- toIndex;fromIndex < toIndex;++ fromIndex, -- toIndex) {
  			long swap = array[fromIndex];
  			array[fromIndex] = array[toIndex];
  			array[toIndex] = swap;
  		}
  	}
  
  	public static void shuffle(int[] array) {
  		java.util.Random rnd = new java.util.Random();
  		for (int i = 0;i < array.length;++ i) {
  			int j = rnd.nextInt(array.length - i) + i;
  			int swap = array[i];
  			array[i] = array[j];
  			array[j] = swap;
  		}
  	}
  
  	public static void shuffle(long[] array) {
  		java.util.Random rnd = new java.util.Random();
  		for (int i = 0;i < array.length;++ i) {
  			int j = rnd.nextInt(array.length - i) + i;
  			long swap = array[i];
  			array[i] = array[j];
  			array[j] = swap;
  		}
  	}
  }
  
  class IntMath {
  
  	public static int gcd(int a, int b) {
  		while (a != 0)
  			if ((b %= a) != 0) a %= b;
  			else return a;
  		return b;
  	}
  
  	public static int gcd(int... array) {
  		int ret = array[0];
  		for (int i = 1; i < array.length; ++i)
  			ret = gcd(ret, array[i]);
  		return ret;
  	}
  
  	public static long gcd(long a, long b) {
  		while (a != 0)
  			if ((b %= a) != 0) a %= b;
  			else return a;
  		return b;
  	}
  
  	public static long gcd(long... array) {
  		long ret = array[0];
  		for (int i = 1; i < array.length; ++i)
  			ret = gcd(ret, array[i]);
  		return ret;
  	}
  
  	public static long lcm(long a, long b) {
  		return a / gcd(a, b) * b;
  	}
  
  	public static int pow(int a, int b) {
  		int ans = 1;
  		for (int mul = a; b > 0; b >>= 1, mul *= mul)
  			if ((b & 1) != 0) ans *= mul;
  		return ans;
  	}
  
  	public static long pow(long a, long b) {
  		long ans = 1;
  		for (long mul = a; b > 0; b >>= 1, mul *= mul)
  			if ((b & 1) != 0) ans *= mul;
  		return ans;
  	}
  
  	public static int pow(int a, long b, int mod) {
  		if (b < 0) b = b % (mod - 1) + mod - 1;
  		long ans = 1;
  		for (long mul = a; b > 0; b >>= 1, mul = mul * mul % mod)
  			if ((b & 1) != 0) ans = ans * mul % mod;
  		return (int)ans;
  	}
  
  	public static int pow(long a, long b, int mod) {
  		return pow((int)(a % mod), b, mod);
  	}
  
  	public static int floorsqrt(long n) {
  		return (int)Math.sqrt(n + 0.1);
  	}
  
  	public static int ceilsqrt(long n) {
  		return n <= 1 ? (int)n : (int)Math.sqrt(n - 0.1) + 1;
  	}
  }
  