#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const long long INFF = 0x3f3f3f3f3f3f3f3fll;
const long long M = 998244353;
const long long maxn = 1.2e6 + 107;
const double pi = acos(-1.0);
const double eps = 0.0000000001;
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
template <typename T>
inline void pr2(T x, unsigned long long k = 64) {
  unsigned long long i;
  for (i = 0; i < k; i++) fprintf(stderr, "%d", (int)((x >> i) & 1));
  putchar(' ');
}
template <typename T>
inline void add_(T &A, int B, long long MOD = M) {
  A += B;
  (A >= MOD) && (A -= MOD);
}
template <typename T>
inline void mul_(T &A, long long B, long long MOD = M) {
  A = (A * B) % MOD;
}
template <typename T>
inline void mod_(T &A, long long MOD = M) {
  A %= MOD;
  A += MOD;
  A %= MOD;
}
template <typename T>
inline void max_(T &A, T B) {
  (A < B) && (A = B);
}
template <typename T>
inline void min_(T &A, T B) {
  (A > B) && (A = B);
}
template <typename T>
inline T abs(T a) {
  return a > 0 ? a : -a;
}
inline long long powMM(long long a, long long b, long long mod = M) {
  long long ret = 1;
  for (; b; b >>= 1ll, a = a * a % mod)
    if (b & 1) ret = ret * a % mod;
  return ret;
}
int startTime;
void startTimer() { startTime = clock(); }
void printTimer() {
  fprintf(stderr, "/--- Time: %ld milliseconds ---/\n", clock() - startTime);
}
int A[maxn], R[maxn], id[maxn];
pair<int, int> ans[maxn];
set<int> Q;
int main() {
  int T, _;
  T = 1;
  for (_ = 1; _ <= T; _++) {
    int n, i, K;
    scanf("%d%d", &n, &K);
    int maxCount = (n + K - 1 - 1) / (K - 1);
    for (i = 1; i <= n * K; i++) scanf("%d", &A[i]);
    for (i = n * K; i >= 1; i--) {
      R[i] = id[A[i]];
      id[A[i]] = i;
    }
    for (i = 1; i <= n * K; i++) {
      if (ans[A[i]].second == i) Q.erase(i);
      if (ans[A[i]].first == 0) ans[A[i]] = make_pair(i, R[i]), Q.insert(R[i]);
      while ((int)Q.size() > maxCount) {
        int x = *Q.rbegin();
        Q.erase(x);
        ans[A[x]] = make_pair(0, 0);
      }
    }
    for (i = 1; i <= n; i++) printf("%d %d\n", ans[i].first, ans[i].second);
  }
}
