#include <bits/stdc++.h>
using namespace std;
int n, k, i, j, ans, val, l, mx = 0;
string s;
int main() {
  cin >> n >> k;
  cin >> s;
  for (i = 0; i < s.size(); ++i) {
    if (s[i] == 'N') {
      ++ans;
      if (ans > k) return cout << "NO\n", 0;
      mx = max(mx, ans);
    } else {
      ans = 0;
    }
  }
  if (mx == k) return cout << "YES\n", 0;
  for (i = 0; i < s.size(); ++i)
    for (j = i; j < s.size(); ++j) {
      val = 0;
      int mx = 0;
      for (l = 0; l < s.size(); ++l)
        if (s[l] == 'N') {
          ++val;
        } else {
          if (s[l] == '?') {
            if (l >= i && l <= j) {
              ++val;
            } else {
              mx = max(mx, val);
              val = 0;
            }
          } else {
            mx = max(mx, val);
            val = 0;
          }
        }
      mx = max(mx, val);
      if (mx == k) return cout << "YES\n", 0;
    }
  return cout << "NO\n", 0;
}
