Recursive GCD

Write a recursive GCD solution that uses the static gcd() helper method and prints the number 15 as the result.

public class RecursiveGCD {
  
  public static void main( String[] args ) {
    System.out.print(gcd(30, 15));
  }
  
  public static int gcd(int m, int n) {
    /* FINISH ME */
    
    return -1;
  }
}