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

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

    long double a[101];
    a[0] = 4;
    a[1] = 3;
    for(int i = 2; i <= 100; i++){
        a[i] = (19*a[i-1] - 12*a[i-2]) / 4.0;
    }

    printf("%.16f\n", a[N]);
}