#include<iostream>
#include<iomanip>
using namespace std;
int main(){
  int wei;
  cin>>wei;
  if(wei<=10){
    cout<<setiosflags(ios::fixed)
        <<setprecision(2)
        <<0.8*wei+0.2
        <<endl;
  }
  else if(wei>10 && wei<=20){
    cout<<setiosflags(ios::fixed)
        <<setprecision(2)
        <<8+0.75*(wei-10)+0.2
        <<endl;
  }
  else if(wei>20 && wei<=30){
    cout<<setiosflags(ios::fixed)
        <<setprecision(2)
        <<8+7.5+0.7*(wei-20)+0.2
        <<endl;
  }
  else{
    cout<<"ÎÞ·¨ÓʼÄ"<<endl;
  }
  return 0;
}