#include <bits/stdc++.h>
using namespace std;
int main(){
	float a,d;
	cin>>a;
	if(a<=10)d=2.5;
	else d=(a-10)*1.5+2.5;
	printf("%.2f",d);
	return 0;
}
/**************************************************************
	Problem: 1043
	User: panyuchen
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/