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

/**************************************************************
	Problem: 1043
	User: tonghuawei
	Language: C++
	Result: Accepted
	Time:23 ms
	Memory:2072 kb
****************************************************************/