#include<iostream>
using namespace std;

int main(){
    double X,Y,N,num,sum=0;
    cin >> X >> Y >> N;
    //X  = X*1000/3600;
    //Y  = Y*1000/3600;
    for(int i=0;i<N;i++){
            cin >> num;
            //cout << (sum+num)/Y << "    " << sum/X << endl;
            if( (sum+num)*X < sum*Y && i!=0){
                cout << "NO\n"; 
                return 0;
            }
            sum+=num;
    }
    cout << "YES\n";
    return 0;
}