03.02.01.Tribonacci

using System;

class Tribonacci
{
    static void Main()
    {
        string input = Console.ReadLine(); //"2 3 4 5";
        string[] inputSplited = input.Split();
        int memberTocheck = int.Parse(inputSplited[3]);

        long[] tribonacciArray = new long[memberTocheck + 1];

        tribonacciArray[0] = 0;
        tribonacciArray[1] = long.Parse(inputSplited[0]);
        tribonacciArray[2] = long.Parse(inputSplited[1]);
        tribonacciArray[3] = long.Parse(inputSplited[2]);

        if (memberTocheck == 1)
        {
            Console.WriteLine(tribonacciArray[1]);
        }
        else if (memberTocheck == 2)
        {
            Console.WriteLine(tribonacciArray[2]);
        }
        else if (memberTocheck == 3)
        {
            Console.WriteLine(tribonacciArray[3]);
        }
        else
        {
            for (int i = 4; i < tribonacciArray.Length; i++)
            {
                tribonacciArray[i] = tribonacciArray[i - 1] + tribonacciArray[i - 2] + tribonacciArray[i - 3];
                if (i == memberTocheck)
                {
                    Console.WriteLine(tribonacciArray[i]);
                    break;
                }
            }
        }
    }
}