#include <iostream>

using namespace std;

int FindStr(int n, int front){
    if(n == 0)  return 1;
    if(front == 1)  return FindStr(n - 1, 0);
    else    return FindStr(n - 1, 0) + FindStr(n - 1, 1);
}


int main(){
    int n;
    cin >> n;

    cout << FindStr(n - 1, 1) + FindStr(n - 1, 0)<< endl;


    return 0;
}