def checker(A, B):
  for i in xrange(len(A)):
    if int(A[i]) > int(B[i]):
      if int(A[i]) == 7 and int(B[i]) == 4:
        print B
        return
      else:
        print A
        return
    elif int(A[i]) < int(B[i]):
      if int(A[i]) == 4 and int(B[i]) == 7:
        print A
        return
      else:
        print B
        return
  print A

A,B = raw_input().split()
if len(A) > len(B):
  print A
elif len(A) < len(B):
  print B
else:
  checker(A,B)