#include <bits/stdc++.h>
using namespace std;
int main(){
	double i,money;
	cin>>i;
	if(i<=15)printf("%.2f",i/1.5);
	else printf("%.2f",20+(i-15)/2.5);
	return 0;
}

/**************************************************************
	Problem: 1052
	User: zhouhongyi
	Language: C++
	Result: Wrong Answer
****************************************************************/