#include "bits/stdc++.h"
using namespace std;
#define print(x) cout<<x<<endl;
#define rep(i,a,b) for(int i=a;i<b;i++)
#define REP(i,a) for(int i=0;i<a;i++)
#define printall(n,array) for(int i=0;i<n;i++){cout<<array[i]<<" ";}cout<<endl;
typedef long long ll;
typedef pair<int, int> PI;
typedef pair<int, PI> V;
typedef vector<int> VE;
const ll mod = 1000000007; //10^9+7

int main(){
  int n;
  cin>>n;
  vector<double> v;
  v.push_back(4);
  v.push_back(3);
  rep(i,2,n+1){
    double a=(19*v[i-1]-12*v[i-2])/4;
    v.push_back(a);
  }
  printf("%.10f\n" , v[n]);
}