#include <bits/stdc++.h>
using namespace std;
int main(){
  cout << fixed << setprecision(20);
  int N;
  cin >> N;
  if (N == 0){
    cout << 4 << endl;
    return 0;
  }
  vector<long double> A(N + 1);
  A[0] = 4;
  A[1] = 3;
  for (int i = 2; i <= N; i++){
    A[i] = A[i - 1] * 19 / 4 - A[i - 2] * 3;
  }
  cout << A[N] << endl;
}