#include <iostream>
#include <iomanip>
using namespace std;
int n;
double x;

void rec(int a,double b,double c){
  double y=(19*b-12*c)/4;
  if(a==n){
    x=y;
  } else {
    rec(a+1,y,b);
  }
}

int main(){
  cin>>n;
  if(n==0){
    x=4;
  } else if(n==1){
    x=3;
  } else {
    rec(2,3,4);
  }
  cout<<fixed<<setprecision(12)<<x<<endl;
  return 0;
}