#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <cstring>
#include <queue>
#include <cmath>
#include <string>
#include <set>
#include <map>

using namespace std;
#define ll long long int
#define rep(i,n) for( int i = 0; i < n; i++ )
#define rrep(i,n) for( int i = n; i >= 0; i-- )
#define REP(i,s,t) for( int i = s; i <= t; i++ )
#define RREP(i,s,t) for( int i = s; i >= t; i-- )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000
#define int long long

signed main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N;
    cin >> N;

    double A[101];
    A[0] = 4;
    A[1] = 3;
    REP(i, 2, N) {
        A[i] = (19 * A[i - 1] - 12 * A[i - 2]) / 4;
    }
    cout << fixed;
    cout << setprecision(10) << A[N] << endl;
    

    return 0;
}