#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}


struct Precision{
  Precision(){
    cout<<fixed<<setprecision(12);
  }
}precision_beet;

//INSERT ABOVE HERE
signed main(){
  vector<double> a({4.0,3.0});

  Int n;
  cin>>n;
  for(Int i=0;i<n;i++){
    double x=(-12*a[i]+19*a[i+1])/4.0;
    a.emplace_back(x);
  }
  
  cout<<a[n]<<endl;
  return 0;
}