using System;

public class Hello
{
    public static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var x = int.Parse(line[0]);
        var y = int.Parse(line[1]);
        var n = int.Parse(Console.ReadLine().Trim());
        line = Console.ReadLine().Trim().Split(' ');
        var a = Array.ConvertAll(line, int.Parse);
        for (int i = 0; i < n-1; i++)
            if (a[i] * y - a[i + 1] * x > 0) { Console.WriteLine("NO"); goto end; }
        Console.WriteLine("YES");
        end:;
    }
}