using System;
using System.Linq;

namespace Lab_7
{
    class Program
    {
        static void Main(string[] args)
        {

            int[] arr1 = Console.ReadLine()
                .Split()
                .Select(int.Parse)
                .ToArray();

            int[] condensed = new int[arr1.Length - 1];
            while (true)
            {
                for (int i = 0; i < condensed.Length - 1; i++)
                {
                    condensed[i] = arr1[i] + arr1[i + 1];


                }
                arr1 = condensed;
                if (arr1.Length == 1)
                { Console.WriteLine(arr1[0]);

                    break;
                }


            }

        }
    }
    }