using System;
using System.Linq;
using System.Text;
using System.Numerics;
using System.Collections;
using System.Collections.Generic;

public class Program {
    static void Main(string[] args) {
        decimal X, Y;
        var _in = Console.ReadLine().Split().Select(x => decimal.Parse(x)).ToList();
        X = _in[0];
        Y = _in[1];
        var N = int.Parse(Console.ReadLine());
        var A = Console.ReadLine().Split().Select(x => decimal.Parse(x)).ToList();
        bool ans = true;
        foreach (var i in Enumerable.Range(0, N - 1)) {
            if (Y / X * A[i] > A[i + 1]) {
                ans = false;
                break;
            }
        }
        Console.WriteLine(ans ? "YES" : "NO");
    }
}