07.FibonacciSum

using System;
using System.Numerics;

class SequenceOfFibonacci
{
    static void Main()
    {
        /* Write a program that reads a number N and calculates the sum of the first N members of the sequence of Fibonacci:
         * 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, … */

        Console.WriteLine("Enter number of members that you want to sum");
        int n = int.Parse(Console.ReadLine());
        BigInteger numOne = 0;
        BigInteger numTwo = 1;
        BigInteger nextNum;
        BigInteger sum = 0;
        for (int i = 0; i <= n-2;i++)
        {
            nextNum = numOne + numTwo;
            numOne = numTwo;
            numTwo = nextNum;
            sum += numOne;
        }
        Console.WriteLine("The sum of first {0} members of sequence of Fibonacci is {1}", n, sum);
    }
}