#include<iostream>
using namespace std;
unsigned long long d[50];
int main() {
    int n, i;
    cin >> n;
    d[1] = 1;
    d[2] = 1;
    for (i = 3; i <= n; i++)
        d[i] = d[i - 1] + d[i - 2];
    cout << 2 * d[n];
    system("pause");
    return 0;
}