#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  int k;
  cin >> n >> k;
  string a;
  cin >> a;
  bool no = false;
  for (int i = 0; i < a.size(); i++) {
    if (a[i] == 'N' && (i + k) <= a.size() && (i == 0 || a[i - 1] != 'N')) {
      int count = 0;
      int j;
      for (j = i; j < i + k; j++) {
        if (a[j] == 'N')
          count++;
        else
          break;
      }
      if (count == k && j < a.size() && a[j] == 'N') {
        cout << "NO";
        return 0;
      }
    }
  }
  for (int i = 0; i < a.size(); i++) {
    if ((i + k) <= a.size() && (i == 0 || a[i - 1] != 'N')) {
      int count = 0;
      int j;
      for (j = i; j < i + k; j++) {
        if (a[j] == '?' || a[j] == 'N')
          count++;
        else
          break;
      }
      if (count == k && (i + k == a.size() || a[j] != 'N')) {
        cout << "YES";
        return 0;
      }
    }
  }
  cout << "NO";
  return 0;
}
