using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Text;
using System.Text.RegularExpressions;
using System.IO;
using System.Linq;

class Program
{
    static void Main()
    {
        new Magatro().Solve();
    }
}

class Magatro
{
    private int X, Y;
    private int N;
    private decimal[] A;
    private void Scan()
    {
        var line = Console.ReadLine().Split(' ');
        X = int.Parse(line[0]);
        Y = int.Parse(line[1]);
        N = int.Parse(Console.ReadLine());
        A = Console.ReadLine().Split(' ').Select(i => int.Parse(i) * 3.6m).ToArray();
    }

    public void Solve()
    {
        Scan();
        decimal sumX = 0;
        decimal sumY = A[0];
        for (int i = 0; i < N - 1; i++)
        {
            sumX += A[i];
            sumY += A[i + 1];
            if (sumX * Y / X > sumY)
            {
                Console.WriteLine("NO");
                return;
            }
        }
        Console.WriteLine("YES");
    }
}