c,y = map(int, input().split())

y = y //100

ce = "can't exchange"
ne = "no exchange"

if (y) < c:
    print(ce)
    exit()

if (y % 5) >= c:
    print(ne)
    exit()

k = y // 5
res = y % 5

need = c-res
r = -(-need // 5) * 5
print(r+res)


# print(k,res,need,r)