import strutils


proc cmpS(a, b: string): int =
  result = 0
  if a == b: return result
  if a.len != b.len: return cmp(a.len, b.len)
  for i in 0..<a.len:
    if a[i] == b[i]: continue
    return cmp(a[i], b[i])


let
  a, b = stdin.readLine.split
  sa = a[0]
  pa = a[1]
  sb = b[0]
  pb = b[1]

echo:
  case cmpS(pa, pb):
  of 0: "-1"
  of 1: sa
  else: sb