#include <bits/stdc++.h>
int res[111];
int only(int l, int r) {
  for (int i = l; i <= r; i++) {
    if (res[i] == 1) {
      return 0;
    }
  }
  return 1;
}
int only1(int l, int r) {
  for (int i = l; i <= r; i++) {
    if (res[i] != -1) {
      return 0;
    }
  }
  return 1;
}
int main() {
  int n, k;
  scanf("%d %d", &n, &k);
  for (int i = 0; i < n; i++) {
    char c;
    scanf("%c", &c);
    while (c == 9 || c == 10 || c == 32) {
      scanf("%c", &c);
    }
    if (c == 'N') {
      if (k == 0) {
        printf("NO");
        return 0;
      } else
        res[i] = -1;
    }
    if (c == '?') {
      res[i] = 0;
    }
    if (c == 'Y') {
      res[i] = 1;
    }
  }
  if (k == 0) {
    printf("YES");
    return 0;
  }
  int ma = 0;
  int fl = 0;
  for (int i = 0; i < n; i++) {
    for (int j = i; j < n; j++) {
      if (only1(i, j))
        if (j - i + 1 > k) {
          printf("NO");
          fl = 1;
          return 0;
        }
    }
  }
  for (int i = 0; i < n; i++) {
    if (i == 0 || res[i - 1] != -1)
      for (int j = i; j < n; j++) {
        if (j == n - 1 || res[j + 1] != -1)
          if (only(i, j))
            if (j - i + 1 == k) {
              printf("YES");
              fl = 1;
              return 0;
            }
      }
  }
  printf("NO");
  return 0;
}
