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

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