#include<bits/stdc++.h>

using namespace std;

#define mod 998244353


int main( void)
{   

      int n; cin >> n;
      long long a[51];
      a[1] = 1; a[2] =2;
      for( int i =3; i<= n; i++)
      {
            a[i] = a[i-1] + a[i-2];
      }
      cout<< a[n];
}