#include <bits/stdc++.h>
using namespace std;
const int oo = 1e9 + 9;
const long long inf = 1e18 + 18;
const int max6 = 1e6 + 6;
const int modx = 1e9 + 123;
const int mody = 997;
const int base = 137;
int t[max6];
int n, k;
bool ok(int l, int r) {
  int cnt = 0;
  for (int i = l; i <= r; ++i) cnt += t[i] == 1;
  if (cnt) return false;
  int cur = 0;
  for (int i = r + 1; i <= n; ++i) {
    if (t[i] == 2)
      cur++;
    else
      cur = 0;
    if (cur > k) return false;
  }
  for (int i = 1; i < l; ++i) {
    if (t[i] == 2)
      cur++;
    else
      cur = 0;
    if (cur > k) return false;
  }
  return true;
}
int main() {
  cin >> n >> k;
  string s;
  cin >> s;
  for (int i = 1; i <= n; ++i)
    if (s[i - 1] == 'Y')
      t[i] = 1;
    else if (s[i - 1] == 'N')
      t[i] = 2;
    else if (s[i - 1] == '?')
      t[i] = 3;
  int res = 0;
  for (int i = 1; i <= n; ++i)
    if (i == 1 || t[i - 1] == 1 || t[i - 1] == 3) {
      int j = i + k - 1;
      if (j == n || t[j + 1] == 1 || t[j + 1] == 3)
        if (ok(i, j)) res = 1;
    }
  cout << (res ? "YES" : "NO");
}
