/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		double a, b, c,f, p = 1.5;
		Scanner x = new Scanner(System.in);
		a=x.nextDouble();
	 	c = a/p;
		b = Math.floor(a/p);
		a = (c-b)*p;
		f = a*a*a-2.25*a;
		System.out.print(f);
	}
}

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

My43

3.7