#include<bits/stdc++.h>
using namespace std;
int main(){
	double n,a;
	cin>>n;
	if(n<=15){
		a=n/1.5;
	} 
	else{
		a=(n-15)/2.5+10;
	}
	cout<<fixed<<setprecision(2)<<a;
	return 0;
}