#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstring>
#include <algorithm>
#include <limits.h>
#include <cmath>
#include <cstdio>
#include <vector>
#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)
using namespace std;

typedef long long ll;
typedef unsigned long long ull;

int main(void)
{
  int i,j,k,l;
  int N;
  long double A[105] = {4,3};
  cin >> N;
  REP(k,2,N+1) {
    A[k] = (19*A[k-1] - 12*A[k-2])/4;
  }
  printf("%.13llf\n",A[N]);
  return 0;
}