#include<iostream>
#include<fstream>
#include<math.h>
#define MAX 500
using namespace std;

ifstream F("nunta.in");
ofstream G("nunta.out");
unsigned int  f(unsigned int i, unsigned int j,unsigned int n,unsigned int k)
{   
    if(k==n)return j;
    else return f(j,j+i,n,k+=1);
       
}

unsigned int n;

int main()
{
  F>>n;
  G<<f(1,1,n,1);
  

   return 0;
}