#include <bits/stdc++.h>

using namespace std;


int main()
{
  int X, Y, N, A[80];

  cin >> X >> Y;
  cin >> N;
  for(int i = 0; i < N; i++) {
    cin >> A[i];
  }

  for(int i = 0; i < N - 1; i++) {
    double t = 1.0 * A[i] / X;
    double far = Y * t;
    if(Y * A[i] > A[i + 1] * X) {
      cout << "NO" << endl;
      return (0);
    }
  }

  cout << "YES" << endl;

}