import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		double a = sc.nextDouble();
		double s;
		if(a<=20){
			s = (double)(a * 1.68);
			System.out.println(String.format("%.2f", s));
		}else if(a > 20){
			s = (double)(a * 1.98);
			System.out.println(String.format("%.2f", s));
		}
		sc.close();
	}

}
/**************************************************************
	Problem: 1643
	User: admin
	Language: Java
	Result: Accepted
	Time:1053 ms
	Memory:40436 kb
****************************************************************/