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

/**************************************************************
	Problem: 1043
	User: chenzelin
	Language: C++
	Result: Wrong Answer
****************************************************************/