#include <bits/stdc++.h>

using namespace std;

int main(void) {
  int x, y, n;
  cin >> x >> y >> n;

  vector<int> a(n);
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }

  bool no = false;
  for (int i = 0; i < n - 1; i++) {
    no |= (a[i] * y > a[i + 1] * x);
  }
  cout << (no ? "NO" : "YES") << endl;

  return 0;
}