#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define all(s) (s).begin(), (s).end()
#define rall(s) (s).rbegin(), (s).rend()
#define rep(i,l,r) for(int i=l;i<r;i++)
#define rrep(i,r,l) for(int i=r;i>l;i--)

using ll=long long;
using mint=modint998244353;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int N;cin>>N;
    vector<long double> A(101);
    A[0]=4;
    A[1]=3;
    rep(i,2,101){
        A[i]=(19*A[i-1]-12*A[i-2])/4;
    }
    cout<<fixed<<setprecision(12)<<A[N]<<endl;
}