def Map():
  return list(map(int,input().split()))

C,Y = Map()
x = Y // 500
r = Y % 500
if r // 100 >= C:
  print('no exchange')
  exit()

c = r // 100 + 5*x
if c < C:
  print('can'+chr(39)+'t'+' exchange')
  exit()

n = (c - C) // 5
c -= n*5
print(c)