#include<iostream>
#include<cstdio>
using namespace std;

int main(){
    int X,Y,N,num,sum=0;
    cin >> X >> Y >> N;
    scanf("%d",&num);
    sum+=num;
    for(int i=1;i<N;i++){
            scanf("%d",&num);
            if( (sum+num)*X < sum*Y){
                cout << "NO\n"; 
                return 0;
            }
            sum+=num;
    }
    cout << "YES\n";
    return 0;
}