#include<bits/stdc++.h>
using namespace std;
int main()
{
int a,b;
cin>>a;
if(a<=10)
{
b=2.5;
}else{
b=2.5+(a-10)*1.5;
}
printf("%.1f",b);
	return 0;
}

/**************************************************************
	Problem: 1641
	User: lzc
	Language: C++
	Result: Wrong Answer
****************************************************************/