public static long gcd(long... values) {
        long res = 0;
        for (long value : values) {
            res = gcd(res, value);
        }
        return res;
    }
@Test
    public void test_calculateGcdN() {
        assertEquals(0, gcd());
        assertEquals(4, gcd(4, 4, 4));
        assertEquals(4, gcd(4, 8, 12));
        assertEquals(1, gcd(4, 8, 13));
    }