#include<bits/stdc++.h>
using namespace std;
int main() {
	int a;
	cin>>a;
	if(a<=10) printf("%.2f",2.5);
	else printf("%.2f",(a-10)*1.5+10*2.5);
}
	
/**************************************************************
	Problem: 1043
	User: linmiaoling
	Language: C++
	Result: Wrong Answer
****************************************************************/