#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;
using ll = long long;


int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    ll x,y;
    cin>>x>>y;
    int n;
    cin>>n;
    vector<ll> a(n);
    for(int i = 0;i<n;i++) cin>>a[i];
    bool fn = false;
    for(int i = 0;i+1<n;i++){
        // a[i] / x > a[i+1] / y
        if(a[i]*y>x*a[i+1]) fn = true;
    }
    if(fn) cout<<"NO\n";
    else cout<<"YES\n";
}