FibonacciNumbers

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _22.FibonacciNumbers
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            if (n==1 || n == 0)
            {
                Console.WriteLine(1);
                return;
            }

            Console.WriteLine(Fib(n));

        }

        static int Fib(int n)
        {
            int x1 = 1;
            int x2 = 1;
            int sum = 0;

            for (int i = 2; i <= n; i++)
            {
                sum = x1 + x2;
                x1 = x2;
                x2 = sum;
            }
            return sum;
        }
    }
}