#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  int a, b;
  cin >> a >> b;
  cin >> s;
  if (s[a + 1] = '_') {
    if (s.size() <= a + b) {
      std::cout << "yes" << std::endl;
    } else {
      std::cout << "no" << std::endl;
    }
  } else {
    std::cout << "no" << std::endl;
  }
}
