#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <map>
#include <set>
#include <algorithm>
#include <functional>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cctype>
#include <string>
#include <cstring>

using namespace std;

typedef long long ll;

bool memo[101];
double x[101];
double rec(int n) {
  if (memo[n]) return x[n];
  memo[n] = true;
  return x[n]=(19*rec(n-1)-12*rec(n-2))/4 < 1e-10 ? 0 : (19*rec(n-1)-12*rec(n-2))/4;
}

int main() {
  x[0] = 4; x[1] = 3;
  memo[0] = true; memo[1] = true;
  
  int n;
  cin >> n;
  double t = rec(n);
  printf("%.10f\n", t);
}