S = gets.chomp.chars
T = gets.chomp.chars

def calc(s, t)
  return '' if s == S.size || t == T.size

  return S[s] + calc(s + 1, t + 1) if S[s] == T[t]

  s2 = calc(s + 1, t)
  t2 = calc(s, t + 1)

  s2.size > t2.size ? s2 : t2
end

print calc(0, 0)
