// GCD.java
// calculate GCD of a and b
// Usage: java GCD a b (a >= b)

public class GCD {

  public static void main (String[] args) {
    
    // check number of arguments
    if (args.length != 2) {
      System.err.println("Usage: java GCD <a> <b>");
      return; // usually, we use System.exit(1);
    }
    
    // initialize a, b
    int a = 0, b = 0;
    
    a = Integer.parseInt(args[0]);
    b = Integer.parseInt(args[1]);
        
    // compute and report the GCD
    System.out.println("The GCD of " + a + " and " + b + " is " + gcd(a, b));
  }

 
  // method to compute the GCD of a and b
  public static int gcd(int a, int b) {

    // if b > a, then swap the two
    if (b > a) {
      int temp = b;
      b = a;
      a = temp;
    }

    // compute initial value of remainder
    int r = a % b;
    
    // iteratively update a, b, r
    while (r != 0) {
      a = b;
      b = r;
      r = a % b;
    }
    
    // return b, the GCD
    return b;
  }
}