#define _USE_MATH_DEFINES
#include<iostream>
#include<vector>
#include<algorithm>
#include<cmath>
#include<string>
#include<iomanip>
#include<numeric>
#include<queue>
#include<deque>
#include<stack>
#include<set>
#include<map>
#include<random>
using namespace std;
typedef long long ll;
const int mod=1e9+7;
int main(){
	int x,y,n,a;
	cin>>x>>y>>n>>a;
	int sum=a;
	while(cin>>a){
		if((sum+a)*x<sum*y)
			cout<<"NO"<<endl,exit(0);
		sum+=a;
	}
	cout<<"YES"<<endl;
}