#include<bits/stdc++.h>
using namespace std;
int main(){
	float n,q;
	cin>>n;
	if(n<=10){
		q=2.5;
	}
	if(n>10){
		q=(n-10)*1.5+2.5;
	}
	printf("%.2f",q);
	return 0;
}

/**************************************************************
	Problem: 1043
	User: huangcanwu
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/