#include <iostream>
#include <iomanip>

using ldouble = long double;

void solve() {
    int n;
    std::cin >> n;

    ldouble a = 4, b = 3;
    while (n--) {
        ldouble c = b * 19 / 4 - a * 3;
        a = b;
        b = c;
    }

    std::cout << a << "\n";
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed << std::setprecision(20);

    solve();

    return 0;
}