import sys
def l(d):
  u = lambda x: {x[i:i+j] for i in range(len(x)) for j in range(len(x) - i + 1)}
  s = u(d[0])
  for v in d[1:]:
    s.intersection_update(u(v))
  return max(s, key=len)
print (l(sys.argv[1:]))