#include<iostream>
#include<string>
#include<cmath>
#include<set>
using namespace std;

int main(){
    int X,Y,N,A[80],num,sum=0;
    cin >> X >> Y >> N;
    for(int i=0;i<N;i++){
            cin >> num;
            if(( ((sum+num)/Y)-(sum/X) ) * (Y-X) > num){
                cout << "NO\n"; 
            }
            sum+=num;
    }
    cout << "YES\n";
    return 0;
}