#include <iostream>

using namespace std;

int x, y, n, a[80];
bool flag = true;

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

	for (int i = 1; i < n; i++){
		if (a[i] * x < a[i - 1] * y){
			flag = false;
		}
	}

	if (flag){
		cout << "YES" << endl;
	}
	else{
		cout << "NO" << endl;
	}

	return 0;
}