using System;
using System.Linq;

namespace PB
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] firstArr = Console.ReadLine().Split().Select(int.Parse).ToArray();

            while(firstArr.Length > 1)
            {
                int[] secondArr = new int[firstArr.Length - 1];
                for (int i = 0; i < firstArr.Length - 1; i++)
                {
                    secondArr[i] = firstArr[i] + firstArr[i + 1];
                }
                firstArr = secondArr;
            }

            Console.WriteLine(firstArr[0]);
        }



    }

}