import java.util.*;
public class Main {
private Scanner sc;
private Main() { this.sc = new Scanner(System.in); }
private void doIt() {
System.out.printf("Input a number: ");
double d = sc.nextDouble();
double res = d;
for(int i=0; i<100; i++) {
res = (res + d / res) / 2;
}
System.out.printf("%.15f\n", res);
}
public static void main(String[] args) { new Main().doIt(); }
}