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

int main( int argc, char *argv[] )
{
int i;
int N;
int X;
int Y;
int A;
int iPre;

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

			return 0;
		}
	}

	cout << "YES" << endl;

	return 0;
}