#include <iostream>
using namespace std;

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

	double b=a[n-1];
	b /= y;
	double c=b*x;
	if(c<=a[n-2]) cout << "NO" << endl;
	else cout << "YES" << endl;

	return 0;
}