Kaprekar Number

This program checks whether a number is Kaprekar number or not.
A number is said to be Kaprekar number if its sum of digits in its square is the number itself.
Example- 9^2 is 81 and 8+1 is 9.So it is a Kaprekar number.
import java.util.*;
public class KaprekarNumbers
{
    public static void main(String args[])
    {
        Scanner ob=new Scanner(System.in);
        System.out.println("Enter number");
        int n=ob.nextInt();
        int N=n*n;
        int tn=n;int c=0;
        while(tn!=0)
        {
            tn=tn/10;c++;
        }
        int q=(int)(N/Math.pow(10,c));
        int r=(int)(N%Math.pow(10,c));
        if(q+r==n)
            System.out.println("Kaprekar number");
        else
            System.out.println("Non Kaprekar number");

  }

}