#include <iostream>
#include <vector>
using namespace std;
int main(){
	int X, Y;
	cin >> X >> Y;
	int N;
	cin >> N;
	vector<int> A(N);
	for (int i = 0; i < N; i++){
		cin >> A[i];
	}
	bool ok = true;
	for (int i = 0; i < N - 1; i++){
		if (A[i] * Y > A[i + 1] * X){
			ok = false;
		}
	}
	if (ok){
		cout << "YES" << endl;
	} else {
		cout << "NO" << endl;
	}
}