Stack_Fibonacci

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

class StackFibonacci
{
    static void Main()
    {
        Stack<long> fibonacii = new Stack<long>();
        int n = int.Parse(Console.ReadLine());
        fibonacii.Push(1);
        fibonacii.Push(1);

        for (int i = 0; i < n - 2; i++)
        {
            long a = fibonacii.Pop();
            long b = fibonacii.Peek();
            fibonacii.Push(a);
            fibonacii.Push(a + b);
        }
        Console.WriteLine(fibonacii.Peek());
    }
}