#include <bits/stdc++.h>
using namespace std;
const int mod = 1000000007;
const int INF = 1000000000;
int n, k, sum[105];
string result = "NO";
int get(int l, int r);
int main() {
  string str;
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> n >> k >> str;
  for (int i = 0; i < n; i++) {
    if (str[i] == 'Y')
      sum[i] = 105;
    else if (str[i] == 'N')
      sum[i] = 1;
  }
  for (int i = 1; i < n; i++) sum[i] += sum[i - 1];
  for (int i = 0; i < n; i++) {
    int j = i + k - 1;
    if (j >= n) break;
    if ((get(i, j) <= k) && ((i == 0) || (str[i - 1] != 'N')) &&
        ((j == n - 1) || (str[j + 1] != 'N')))
      result = "YES";
  }
  for (int i = 0; i < n; i++) {
    int j = i + k;
    if (j >= n) break;
    if (get(i, j) == k + 1) result = "NO";
  }
  cout << result << "\n";
  return 0;
}
int get(int l, int r) {
  if (l == 0) return sum[r];
  return sum[r] - sum[l - 1];
}
