using System;
using System.Collections.Generic;
using System.Linq;

namespace _01._Sum_Adjacent_Equal_Numbers
{
    internal class Program
    {
        static void Main(string[] args)
        {
            List<double> numbers = Console.ReadLine()
                .Split(" ", StringSplitOptions.RemoveEmptyEntries)
                .Select(double.Parse)
                .ToList();

            for (int i = 0; i < numbers.Count - 1; i++)
            {
                double currentIndex = numbers[i];
                double nextIndex = numbers[i + 1];

                if (currentIndex + nextIndex == numbers[i])
                {
                    double result = numbers[i] + currentIndex + nextIndex;
                    Console.WriteLine(result);
                }
            }
        }
    }
}