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

int main()
{
int i;
int X;
int Y;
int N;
int iPre;
int iNow;

	cin >> X;
	cin >> Y;
	cin >> N;
	iPre = 0;
	for( i = 0; i < N; i++ )
	{
		cin >> iNow;
		if( iPre * Y > iNow * X )
		{
			cout << "NO" << endl;

			return 0;
		}
		
		iPre = iNow;
	}

	cout << "YES" << endl;

	return 0;
}