//
//  GCDtest.java
//
//  Class GCDtest implements the Euclidean algorithm for finding the
//    greatest common divisor: int gcd(int x, int y)
//  The program takes two integer arguments from the command line x and y
//    and returns the gcd(x,y)


class GCDtest {

    private final static String USAGE  = "Usage: java GCDtest x y";
    
    public static void main(String[] args) {
	
	// test number of input arguments
	if (args.length != 2) {
	    System.err.println(USAGE);
            System.exit(-1);
	}

	try {
	    // read in command line input
	    int x = java.lang.Integer.parseInt(args[0]);
	    int y = java.lang.Integer.parseInt(args[1]);

	    // calculate and print gcd recusively
	    System.out.println(gcd(x,y));
	    
	} catch (NumberFormatException ex) {
	    System.out.println(USAGE);
            System.exit(-1);
	}
    }

    // recursive algorithm to calculate the greatest common divisor of two integers
    private static int gcd(int x, int y) {
	if (y != 0) 
	    return gcd (y, x % y);
	else
	    return java.lang.Math.abs(x);
    }
}