#include<iostream>
#include <iomanip> 
using namespace std;
int main(){
	double m,n;
	cin>>m;
	if(m<=15){
		n=m/1.5; 
	}else{
		n=(m-15)/2.5+10;
	}
	cout<<fixed<<setprecision(2)<<n; 
	return 0;
}
/**************************************************************
	Problem: 1052
	User: admin
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/