def gcd(a,b):
  assert int(a) == a and int(b) == b, "The numbers must be positive integers only"
  if a < 0:
    a = -1 * a
  if b < 0:
    b = -1 * b
  if b == 0:
    return a
  else:
    return gcd(b, a%b)

print(gcd(12,48))
