euclidean algorithm

import static java.lang.System.out;

final class Main {
    public static void main(String[] args) {
        out.println(euclideanAlgorithm(20, 40));
    }
    
    private static int euclideanAlgorithm(int a, int b) {
        return b == 0 ? a : euclideanAlgorithm(b, a % b);
    }
}