using System;
using System.Linq;

public class Solution
{
    public static void Main()
    {
        var vals = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
        int x = vals[0];
        int y = vals[1];

        Console.ReadLine();
        var a = Console.ReadLine().Split(' ').Select(int.Parse).ToList();
        a.Insert(0, 0);

        bool lost = false;
        for (int i = 1; i < a.Count; i++)
        {
            /*
            var xPos = a[i - 1];
            var t = xPos / (double)x;
            var yPos = y * t;
            */
            if (y*a[i-1] > x*a[i]) // 誤差対策 yPos > a[i]を変形
            {
                lost = true;
                break;
            }
        }

        Console.WriteLine(lost ? "NO" : "YES");
    }
}