#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include<iomanip>
using namespace std;
#ifdef _WIN32
#include <Windows.h>
#endif

int main()
{
    int x, y, n, t1;
    double a, b;
    cin >> x >> y >> n >> t1;
    a = 1.*y/x;
    for (int i = 0; i < n-1; i++){
        int t2;
        cin >> t2;
        b = 1.*t2/t1;
        if (a > b){
            cout << "NO" << endl;
            return 0;
        }
        t1 = t2;
    }
    cout << "YES" << endl;
}