#include <iostream>
using namespace std;

int x, y;
int n;
int a[80];

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