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