#include <bits/stdc++.h>
using namespace std;

int main() {
  int X, Y, N, A, B;
  cin >> X >> Y >> N >> A;
  while (cin >> B) {
    if (B * X < A * Y) return cout << "NO" << "\n", 0;
    A = B;
  }
  cout << "YES" << "\n";
}