#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float q;
	cin>>n;
	if (n<=10){
		q=2.5;
	} 
	else {
		q=(n-10)*1.5+2.5;
	}
	printf("%.2f",q);
}
/**************************************************************
	Problem: 1043
	User: chenyichuen
	Language: C++
	Result: Accepted
	Time:22 ms
	Memory:2072 kb
****************************************************************/