#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;
using ll = long long;

#include<iomanip>
int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int n;
    cin>>n;
    if(n==0) cout<<4<<endl;
    else if(n==1) cout<<3<<endl;
    else{
        long double a = 4;
        long double b = 3;
        for(int i = 2;i<=n;i++){
            long double c = 19 * b - 12 * a;
            c /= 4;
            a = b;
            b = c;
        }
        cout<<setprecision(30)<<fixed<<b<<endl;
    }
}