source_code: import java.util.*;
  import java.io.*;
  
  public class RGBSubstring {
      public static void main(String[] args) {
          FastScanner scanner = new FastScanner();
          PrintWriter out = new PrintWriter(System.out);
          int Q = scanner.nextInt();
          while(Q-->0) {
              int N = scanner.nextInt();
              int K = scanner.nextInt();
              String s1 = "RGB";
              String s2 = "GBR";
              String s3 = "BRG";
              char[] arr = scanner.next().toCharArray();
              int[] cnts = new int[3];
              for(int i = 0; i < K; i++) {
                  int ind = i % 3;
                  if (arr[i] != s1.charAt(ind)) cnts[0]++;
                  if (arr[i] != s2.charAt(ind)) cnts[1]++;
                  if (arr[i] != s3.charAt(ind)) cnts[2]++;
              }
              int ans = Math.min(Math.min(cnts[0], cnts[1]), cnts[2]);
              for(int i = K; i < N; i++) {
                  int ind = (K-1)%3;
                  int[] nextCnts = new int[3];
                  nextCnts[1] = cnts[0];
                  nextCnts[2] = cnts[1];
                  nextCnts[0] = cnts[2];
                  if ('R' != arr[i-K]) nextCnts[1]--;
                  if ('G' != arr[i-K]) nextCnts[2]--;
                  if ('B' != arr[i-K]) nextCnts[0]--;
                  if (arr[i] != s1.charAt(ind)) nextCnts[0]++;
                  if (arr[i] != s2.charAt(ind)) nextCnts[1]++;
                  if (arr[i] != s3.charAt(ind)) nextCnts[2]++;
                  cnts = nextCnts;
                  for(int j = 0; j < 3; j++) ans = Math.min(ans, cnts[j]);
              }
              out.println(ans);
          }
          out.flush();
      }
      
      public static class FastScanner {
          BufferedReader br;
          StringTokenizer st;
          
          public FastScanner(Reader in) {
              br = new BufferedReader(in);
          }
          
          public FastScanner() {
              this(new InputStreamReader(System.in));
          }
          
          String next() {
              while (st == null || !st.hasMoreElements()) {
                  try {
                      st = new StringTokenizer(br.readLine());
                  } catch (IOException e) {
                      e.printStackTrace();
                  }
              }
              return st.nextToken();
          }
          
          int nextInt() {
              return Integer.parseInt(next());
          }
          
          long nextLong() {
              return Long.parseLong(next());
          }
          
          double nextDouble() {
              return Double.parseDouble(next());
          }
          
          String readNextLine() {
              String str = "";
              try {
                  str = br.readLine();
              } catch (IOException e) {
                  e.printStackTrace();
              }
              return str;
          }
          
          int[] readIntArray(int n) {
              int[] a = new int[n];
              for (int idx = 0; idx < n; idx++) {
                  a[idx] = nextInt();
              }
              return a;
          }
      }
  }
  