#include <bits/stdc++.h>
using namespace std;
int main(){
   float n,t=0,s=0; 
   cin>>n;
   if(n<=10) s=2.5;
   else{
   	t=n-10;
   	s=t*1.5+2.5;
   } 
printf("%.2f",s);
}

/**************************************************************
	Problem: 1043
	User: huangluowei
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/