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

/**************************************************************
	Problem: 1043
	User: toughuatao1
	Language: C++
	Result: Accepted
	Time:19 ms
	Memory:2072 kb
****************************************************************/