#include<iostream>
#include<algorithm>
#include<string>
#include<vector>
using namespace std;
long long X, Y, N, a[100000];
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 + 1] * X < a[i] * Y) { cout << "NO" << endl; return 0; }
	}
	cout << "YES" << endl;
	return 0;
}