using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(Fib(7,new Dictionary<int,int>()).ToString());

    }

    public static int Fib(int n,Dictionary<int,int> d){

        if(n==0 || n==1){

            if(d==null)

                d=new Dictionary<int,int>();

            if(!d.ContainsKey(n)){

                d.Add(n,n);

                //Console.Write(n.ToString()+",");

            }

            return n;

        }

        if(d.ContainsKey(n))

            return d[n];

        int fibn=Fib(n-1,d)+Fib(n-2,d);

        if(n>2)

            d.Remove(n-2);

        d.Add(n,fibn);

        //Console.Write(fibn.ToString()+",");

        return fibn;        

    }

}