To reduce integer as single digit

Write a program to read an integer and reduce it to a single digit

import java.util.Scanner;
public class DigitReduce
 {
 public static void main(String[] args)
 {
  Scanner sc=new Scanner(System.in);
  System.out.println("Enter a Number:-");    
  long num=sc.nextLong();
  System.out.println(" " + calculateDigit(num));
 }
 private static long calculateDigit(long num)
 {
  return (num/10 == 0 ? num : calculateDigit(num/10 + num % 10));
 }
 }


Output:

Enter a Number:-

4789
1


Enter a Number:-

3348
9