import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double x = sc.nextDouble();
		double a = x * 0.8;
		double b = x * 0.9;
		double p =(double) (x + a + b) / 3;
		System.out.println(String.format("%.1f", p));
	}
}
/**************************************************************
	Problem: 1613
	User: admin
	Language: Java
	Result: Accepted
	Time:809 ms
	Memory:40732 kb
****************************************************************/