using System;
using System.Linq;
class Program {
    static void Main() {
        int[] xy = Console.ReadLine().Split().Select(int.Parse).ToArray();
        int x = xy[0], y = xy[1];
        int n = int.Parse(Console.ReadLine());
        int[] As = Console.ReadLine().Split().Select(int.Parse).ToArray();
        string ans = "YES";
        for (int i = 0; i < n - 1; i++) {
            if (As[i + 1] * x < As[i] * y) {
                ans = "NO";
                break;
            }
        }
        Console.WriteLine(ans);
    }
}