#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e17L;
const int inf = 0x3f3f3f3f;
const int maxn = 1e2 + 5;
const int Mod = 1e9 + 7;
int dp[maxn][maxn][maxn], n, k;
string s;
int main() {
  cin >> n >> k >> s;
  dp[0][0][0] = 1;
  for (int i = 1; i <= n; i++) {
    char c = s[i - 1];
    for (int j = 0; j <= k; j++) {
      for (int d = 0; d <= j; d++) {
        if (dp[i - 1][j][d]) {
          if (c == 'Y') {
            dp[i][j][0] = 1;
          } else if (c == 'N') {
            dp[i][max(j, d + 1)][d + 1] = 1;
          } else {
            dp[i][max(j, d + 1)][d + 1] = 1;
            dp[i][j][0] = 1;
          }
        }
      }
    }
  }
  bool flag = false;
  for (int i = 0; i <= k; i++)
    if (dp[n][k][i]) flag = true;
  if (flag)
    puts("YES");
  else
    puts("NO");
  return 0;
}
