#include <bits/stdc++.h>
int dp[101][101][2], n, k;
char s[101];
int solve(int i, int j, int b) {
  if (j == k) b = 1;
  if (j > k) return 0;
  if (i == n) return b;
  if (dp[i][j][b] != -1) return dp[i][j][b];
  int ans = 0;
  if (s[i] == 'Y')
    ans = solve(i + 1, 0, b);
  else if (s[i] == 'N')
    ans = solve(i + 1, j + 1, b);
  else
    ans = solve(i + 1, 0, b) | solve(i + 1, j + 1, b);
  return dp[i][j][b] = ans;
}
int main() {
  scanf("%d %d", &n, &k);
  scanf(" %s", s);
  memset(dp, -1, sizeof(dp));
  if (solve(0, 0, 0))
    printf("YES");
  else
    printf("NO");
  return 0;
}
