#include <bits/stdc++.h>

using namespace std;

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  vector<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;
  }

  int n;
  cin >> n;
  cout << fixed << setprecision(10) << a[n] << endl;
  
  return 0;
}