import strutils
proc echoNG = echo "NG"; quit()

let A, B = stdin.readLine
var flgNG: bool

for AorB in [A, B]:
  if AorB.len != 1 and AorB[0] == '0':
    echoNG()

  for c in AorB:
    if not c.isDigit:
      echoNG()


echo "OK"