import java.util.Scanner;
public class Main
{   
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int x = sc.nextInt();
        double a = x*5.0;
        double b = x*4.5;
        double c = x*4.0;
        double d = x*3.5;
        if(x>10) {
        	System.out.println(d);
        }else if(x>=6) {
        	System.out.println(c);
        }else if(x>=2) {
        	System.out.println(b);
        }else {
        	System.out.println(a);
        }
       
    
    }
}
/**************************************************************
	Problem: 1717
	User: admin
	Language: Java
	Result: Accepted
	Time:4163 ms
	Memory:40476 kb
****************************************************************/