#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	if(n>10) printf("%.1f",n*3.5);
	else if(n>=6&&n<=10) printf("%.1f",n*4.0);
	else if(n>=2&&n<=5) printf("%.1f",n*4.5);
	else printf("%.1f",n*5.0);
}
/**************************************************************
	Problem: 1717
	User: linzihang
	Language: C++
	Result: Accepted
	Time:48 ms
	Memory:2072 kb
****************************************************************/