#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
const long long int INF = 1e12;
int n, k;
int memo[101][101][101];
int solve(string &str, int i, int N, int _max) {
  _max = max(N, _max);
  int &a = memo[i][N][_max];
  if (a != -1) return a;
  if (i == n) {
    if (_max == k) return a = 1;
    return a = 0;
  }
  if (str[i] == 'Y')
    return a = solve(str, i + 1, 0, _max);
  else if (str[i] == 'N')
    return a = solve(str, i + 1, N + 1, _max);
  else {
    if (solve(str, i + 1, 0, _max)) return a = 1;
    return a = solve(str, i + 1, N + 1, _max);
  }
  return a = 0;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  memset(memo, -1, sizeof(memo));
  cin >> n >> k;
  string str;
  cin >> str;
  if (solve(str, 0, 0, 0))
    cout << "YES";
  else
    cout << "NO";
  return 0;
}
