//by sweecrow 2018
import java.util.Scanner;

public class Main {
	
	public static void main(String[] args) {
		
		Scanner in = new Scanner(System.in); 
		int tal = in.nextInt();
		
		//Prints out result from formula
		System.out.println((5.0/9) * (tal - 32));
		
	}

}