using System;
using System.Linq;

class Program
{
    static void Main()
    {

        int[] mainMasiv = Console.ReadLine().Split().Select(int.Parse).ToArray();
        int[] condensedMasiv = new int[mainMasiv.Length - 1];

        if (mainMasiv.Length == 1)
        {
            Console.WriteLine(mainMasiv[0]);
            return;
        }

        for (int i = 0; i < mainMasiv.Length; i++)
        {
            for (int j = 0; j < condensedMasiv.Length - i; j++)
            {
                condensedMasiv[j] = mainMasiv[j] + mainMasiv[j + 1];
            }
            mainMasiv = condensedMasiv;
        }
        Console.WriteLine(condensedMasiv[0]);
    }
}