#include<iostream>
#include<iomanip>
using namespace std;
int main(){
	double x,i;
	cin>>i;
	if(i<=10){
		x=2.5;
	}else if(i>10){
		x=2.5+(i-10)*1.5;
	}
	cout<<fixed<<setprecision(2)<<x<<endl;
}
/**************************************************************
	Problem: 1043
	User: admin
	Language: C++
	Result: Accepted
	Time:17 ms
	Memory:2072 kb
****************************************************************/