#include <bits/stdc++.h>
using namespace std;

int Pell(int x)
{
    int i = 1, P0 = 2, P1 = 2, Pn = 2;
    do
    {
        int tmp = Pn;
        Pn = 2*Pn+P1;
        P0 = P1;
        P1 = tmp;
        i++;
    }
    while (i <= x);

    return P1;
}

int main()
{
    ios_base::sync_with_stdio(0);
    int n;

    cin >> n;

    cout << Pell(n) << endl;
    return 0;
}