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

/**************************************************************
	Problem: 1043
	User: sucongyi
	Language: C++
	Result: Accepted
	Time:20 ms
	Memory:2072 kb
****************************************************************/