[SoftUni C# exam preparation] 02.Tribonacci

using System;
using System.Numerics;

    class Tribonacci
    {
        static void Main()
        {
            BigInteger trib1 = new BigInteger(Int32.Parse(Console.ReadLine()));
            BigInteger trib2 = new BigInteger(Int32.Parse(Console.ReadLine()));
            BigInteger trib3 = new BigInteger(Int32.Parse(Console.ReadLine()));
            int n = Int32.Parse(Console.ReadLine());

            if (n == 1)
            {
                Console.WriteLine(trib1);
            }
            else if (n == 2)
            {
                Console.WriteLine(trib2);
            }
            else if (n == 3)
            {
                Console.WriteLine(trib3);
            }
            else
            {
                for (int i = 4; i <= n; i++)
                {
                    BigInteger tribNew = trib1 + trib2 + trib3;
                    trib1 = trib2;
                    trib2 = trib3;
                    trib3 = tribNew;
                }
                Console.WriteLine(trib3);
            }
        }
    }