#include <cmath>
#include <string>
#include <vector>
#include <iomanip>
#include <iostream>
#include <algorithm>
#include <functional>
#pragma warning(disable : 4996)
using namespace std;
int X, Y, N, A[80];
int main() {
	scanf("%d %d", &X, &Y);
	scanf("%d", &N);
	for (int i = 0; i < N; i++) scanf("%d", &A[i]);
	bool flag = true;
	for (int i = 0; i < N - 1; i++) {
		if (X * A[i + 1] < Y * A[i]) flag = false;
	}
	printf(flag ? "YES\n" : "NO\n");
	return 0;
}