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

int main(){
    int in,pre,n,vx,vy;
    cin >> vx >> vy >> n;

    cin >> pre;
    while(cin >> in){
        if(in*vx<pre*vy){
            cout << "NO" << endl;
            return 0;
        }
        pre=in;
    }
    
    cout << "YES" << endl;

    return 0;
}