using System;

​

public class Program

{

    public static void Main()

    {

        string input = Console.ReadLine();

        string[] parts = input.Split(' ', StringSplitOptions.RemoveEmptyEntries);

        int[] num = new int[parts.Length];

        for (int i = 0; i < parts.Length; i++)

        {

            num[i] = int.Parse(parts[i]);

        }

​

        if (num.Length == 1)

        {

            Console.WriteLine(num[0]);

            return;

        }

​

        while (num.Length > 1)

        {

            int[] condensed = new int[num.Length - 1];

            for (int i = 0; i < condensed.Length; i++)

            {

                condensed[i] = num[i] + num[i + 1];

            }

​

            num = condensed;

        }

​

        Console.WriteLine(num[0]);

    }

}