Crossing Sequences

using System;
using System.Numerics;


namespace CrossingSequences
{
    class CrossingSequences
    {
        const int size = 1000000;
        public static bool GetTribonacci(BigInteger firstTribNum, BigInteger secondTribNum,
                                        BigInteger thirdTribNum, BigInteger spiralStart)
        {
            BigInteger tribonacci = firstTribNum + secondTribNum + thirdTribNum;
            if (firstTribNum > spiralStart)
            {
                return false;
            }
            if ((firstTribNum == spiralStart) && (firstTribNum <= size))
            {
                return true;
            }
            BigInteger a = secondTribNum;
            BigInteger b = thirdTribNum;
            BigInteger c = tribonacci;

            return GetTribonacci(a, b, c, spiralStart);
        }

        public static void Main()
        {
            int firstTribNum = int.Parse(Console.ReadLine());
            int secondTribNum = int.Parse(Console.ReadLine());
            int thirdTribNum = int.Parse(Console.ReadLine());

            int spiralStart = int.Parse(Console.ReadLine());
            int spiralStep = int.Parse(Console.ReadLine());
            bool checkForEquals = false;

            int counter = 0;
            int step = spiralStep;

            for (int i = spiralStart; i <= size; i++)
            {
                checkForEquals = GetTribonacci(firstTribNum, secondTribNum, thirdTribNum, spiralStart);
                if (checkForEquals)
                {
                    Console.WriteLine(spiralStart);
                    return;
                }
                if ((counter >= 2) && (counter % 2 == 0))
                {
                    spiralStep += step;
                }

                spiralStart += spiralStep;

                counter++;
            }
            Console.WriteLine("No");
        }
    }
}