#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: wengzihang
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/