#include <bits/stdc++.h>
using namespace std;

int main()
{
	int X, Y, N;
	cin >> X >> Y >> N;
	vector<int> A( N );
	for( int i = 0; i < N; i++ ) {
		cin >> A[i];
	}

	int flag = 0;
	for( int i = 1; i < N ; i++ ) {
		long long a = A[i];
		long long a1 = A[i - 1];
		if( a * X < a1 * Y ) {
			flag = 1;
			break;
		}
	}
	string ans = "YES";
	if( flag ) ans = "NO";

	cout << ans << endl;
}