using System.Console;

using System.Math;

public class Program {

    public static void Main() {

        WriteLine(Fib(8));

        WriteLine(FibIte(8));

        WriteLine(FibRec(8));

    }

    static ulong Fib(int n) {

​

        double sqrt5 = Sqrt(5);

        double p1 = (1 + sqrt5) / 2;

        double p2 = -1 * (p1 - 1);

        double n1 = Pow(p1, n);

        double n2 = Pow(p2, n);

        return (ulong)((n1 - n2) / sqrt5);

    }

    static int FibIte(int n) {

        int a = 0;

        int b = 1;

        for (int i = 0; i < n; i++) {

            int temp = a;

            a = b;

            b = temp + b;

        }

        return a;

    }

    static int FibRec(int n) {

        if (n < 2) {

            return n;

        } else {

            return FibRec(n - 1) + FibRec(n - 2);

        }

    }

}