#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <cstdio>
#include <ctime>
#include <assert.h>
#include <chrono>
#include <random>
#include <numeric>
#include <set>
using namespace std;
typedef long long int ll;
using ull = unsigned long long;

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    bool ok=1;
    ll x,y; cin >> x >> y;
    int n; cin >> n;
    vector<ll> a(n);
    for(int i=0;i<n;i++){
        cin >> a[i];
    }
    for(int i=0;i+1<n;i++){
        if(y*a[i]>x*a[i+1])ok=0;
    }
    if(ok)printf("YES\n");
    else printf("NO\n");
}