import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		double s;
		if(n <= 10){
			s = 2 * n;
			System.out.println(String.format("%.1f", s));
		}else if(n > 10){
			s = 2 * n * 0.9;
			System.out.println(String.format("%.1f", s));
		}
		sc.close();
	}

}
/**************************************************************
	Problem: 1636
	User: admin
	Language: Java
	Result: Accepted
	Time:1158 ms
	Memory:40232 kb
****************************************************************/