description: Consider a sequence of integers a_1, a_2, …, a_n. In one move, you can select any element of the sequence and delete it. After an element is deleted, all elements to the right are shifted to the left by 1 position, so there are no empty spaces in the sequence. So after you make a move, the sequence's length decreases by 1. The indices of the elements after the move are recalculated.
  
  E. g. let the sequence be a=[3, 2, 2, 1, 5]. Let's select the element a_3=2 in a move. Then after the move the sequence will be equal to a=[3, 2, 1, 5], so the 3-rd element of the new sequence will be a_3=1 and the 4-th element will be a_4=5.
  
  You are given a sequence a_1, a_2, …, a_n and a number k. You need to find the minimum number of moves you have to make so that in the resulting sequence there will be at least k elements that are equal to their indices, i. e. the resulting sequence b_1, b_2, …, b_m will contain at least k indices i such that b_i = i.
  
  Input
  
  The first line contains one integer t (1 ≤ t ≤ 100) — the number of test cases. Then t test cases follow.
  
  Each test case consists of two consecutive lines. The first line contains two integers n and k (1 ≤ k ≤ n ≤ 2000). The second line contains a sequence of integers a_1, a_2, …, a_n (1 ≤ a_i ≤ n). The numbers in the sequence are not necessarily different.
  
  It is guaranteed that the sum of n over all test cases doesn't exceed 2000.
  
  Output
  
  For each test case output in a single line:
  
    * -1 if there's no desired move sequence; 
    * otherwise, the integer x (0 ≤ x ≤ n) — the minimum number of the moves to be made so that the resulting sequence will contain at least k elements that are equal to their indices. 
  
  Example
  
  Input
  
  
  4
  7 6
  1 1 2 3 4 5 6
  5 2
  5 1 3 2 3
  5 2
  5 5 5 5 4
  8 4
  1 2 3 3 2 2 5 5
  
  
  Output
  
  
  1
  2
  -1
  2
  
  Note
  
  In the first test case the sequence doesn't satisfy the desired condition, but it can be provided by deleting the first element, hence the sequence will be [1, 2, 3, 4, 5, 6] and 6 elements will be equal to their indices.
  
  In the second test case there are two ways to get the desired result in 2 moves: the first one is to delete the 1-st and the 3-rd elements so that the sequence will be [1, 2, 3] and have 3 elements equal to their indices; the second way is to delete the 2-nd and the 3-rd elements to get the sequence [5, 2, 3] with 2 desired elements.
solution: import java.io.*;
  import java.util.*;
  import java.math.BigInteger;
  import java.util.InputMismatchException;
  
  public class Main {
  	static PrintWriter out;
  	static Reader in;
  	public static void main(String[] args) throws IOException {
  		input_output();
  		Main solver = new Main();
  		solver.solve();
  		out.close();
  
  		out.flush();
  	} 
  
  	static long INF = (long)1e18;
  	static int MAXN = (int)1e5 + 5;
  	static int MOD = (int)1e9 + 7;
  	static int q, t, n, m, k;
  	static double pi = Math.PI;
  
  	void solve() throws IOException {
  		t = in.nextInt();
  		
  
  		while (t --> 0) {
  			n = in.nextInt();
  			k = in.nextInt();
  
  			int[] arr = new int[n+1];
  			for (int i = 1; i <= n; i++) arr[i] = in.nextInt();
  
  			int[][] dp = new int[n+1][n+2];
  
  			for (int i = 1; i <= n; i++) {
  				for (int j = 0; j <= n; j++) {
  					dp[i][j] = Math.max(dp[i][j], dp[i-1][j]+(j == i-arr[i] ? 1: 0));
  					dp[i][j+1] = Math.max(dp[i][j+1], dp[i-1][j]);
  				}
  
  			}
  
  
  			int ans = -1;
  			for (int i = 0; i <= n; i++) {
  				if (dp[n][i] >= k) {
  					ans = i;
  					break;
  				}
  			}
  
  			out.println(ans);
  		}	
  	}
  
  	static class Reader {
  		private InputStream mIs;
  		private byte[] buf = new byte[1024];
  		private int curChar;
  		private int numChars;
  
  		public Reader() {
  			this(System.in);
  		}
  
  		public Reader(InputStream is) {
  			mIs = is;
  		}
  
  		public int read() {
  			if (numChars == -1) {
  				throw new InputMismatchException();
  
  			}
  			if (curChar >= numChars) {
  				curChar = 0;
  				try {
  					numChars = mIs.read(buf);
  				} catch (IOException e) {
  					throw new InputMismatchException();
  				}
  				if (numChars <= 0) {
  					return -1;
  				}
  			}
  			return buf[curChar++];
  		}
  
  		public String nextLine() {
  			int c = read();
  			while (isSpaceChar(c)) {
  				c = read();
  			}
  			StringBuilder res = new StringBuilder();
  			do {
  				res.appendCodePoint(c);
  				c = read();
  			} while (!isEndOfLine(c));
  			return res.toString();
  		}
  
  		public String next() {
  			int c = read();
  			while (isSpaceChar(c)) {
  				c = read();
  			}
  			StringBuilder res = new StringBuilder();
  			do {
  				res.appendCodePoint(c);
  				c = read();
  			} while (!isSpaceChar(c));
  			return res.toString();
  		}
  
  		double nextDouble() {
  			return Double.parseDouble(next());
  		}
  
  		public long nextLong() {
  			int c = read();
  			while (isSpaceChar(c)) {
  				c = read();
  			}
  			int sgn = 1;
  			if (c == '-') {
  				sgn = -1;
  				c = read();
  			}
  			long res = 0;
  			do {
  				if (c < '0' || c > '9') {
  					throw new InputMismatchException();
  				}
  				res *= 10;
  				res += c - '0';
  				c = read();
  			} while (!isSpaceChar(c));
  			return res * sgn;
  		}
  
  		public int nextInt() {
  			int c = read();
  			while (isSpaceChar(c)) {
  				c = read();
  			}
  			int sgn = 1;
  			if (c == '-') {
  				sgn = -1;
  				c = read();
  			}
  			int res = 0;
  			do {
  				if (c < '0' || c > '9') {
  					throw new InputMismatchException();
  				}
  				res *= 10;
  				res += c - '0';
  				c = read();
  			} while (!isSpaceChar(c));
  			return res * sgn;
  		}
  
  		public boolean isSpaceChar(int c) {
  			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
  		}
  
  		public boolean isEndOfLine(int c) {
  			return c == '\n' || c == '\r' || c == -1;
  		}
  
  	}
  	static void input_output() throws IOException {
  		File f = new File("in.txt");
  		if (f.exists() && !f.isDirectory()) {
  			in = new Reader(new FileInputStream("in.txt"));
  		} else in = new Reader();
  		f = new File("out.txt");
  		if (f.exists() && !f.isDirectory()) {
  			out = new PrintWriter(new File("out.txt"));
  		} else out = new PrintWriter(System.out);
  	}
  }