using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace task_5
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] nums = Console.ReadLine()
                           .Split()
                           .Select(s => int.Parse(s))
                           .ToArray();
            int n = nums.Length;
            int i = 0;
            for (int j = (n - 1) * (n - 1); j > 0; i++, j--)
            {
                if (i == n - 1)
                {
                    i = 0;
                }
                int[] condensed = new int[n];
                condensed[i] = nums[i] + nums[i + 1];
                nums[i] = condensed[i];
            }
            int result = nums[0];
            Console.WriteLine(result);
        }
    }
}