#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int x, y, n;
  cin >> x >> y >> n;
  vector<int> a(n);
  rep(i, n) cin >> a[i];
  rep(i, n-1) {
    if (y * a[i] > a[i + 1] * x) {
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
  return 0;
}