def main():
    c, y = map(int, input().split())
    y = y // 100
    cur = y % 5

    while cur < c and cur < y:
        cur += 5

    if c > cur:
        print("can't exchange")
    elif cur == y % 5:
        print("no exchange")
    else:
        print(cur)


if __name__ == '__main__':
    main()