#include"bits/stdc++.h"
using namespace std;
int main() {
	int k, u, n; cin >> k >> u >> n;
	vector<int> a(n);
	for (int i = 0; i < n; i++)cin >> a[i];
	bool b = true;
	for (int i = 1; i < n; i++) {
		if (k * a[i] < a[i - 1] * u) {
			b = false;
			break;
		}
	}
	cout << (b ? "YES" : "NO") << endl;
}