#include <bits/stdc++.h>
using namespace std;
int main(){
	int a;
	float s;
	cin>>a;
	if(a<=1){
		s=a*5;
	}
	if(a<=5&&a>=2){
		s=a*4.5;
	}
	if(a<=10&&a>=6){
		s=a*4;
	}
	if(a>10){
		s=a*3.5;
	}printf("%.1f",s);
}

/**************************************************************
	Problem: 1717
	User: tonghuawei
	Language: C++
	Result: Accepted
	Time:38 ms
	Memory:2072 kb
****************************************************************/