def exchange(C, Y):
    coins = [0]*10
    currency = [1, 5, 10, 50, 100, 500, 1000, 2000, 5000, 10000]
    
    for i in range(9, -1, -1):
        coins[i] = Y // currency[i]
        Y %= currency[i]
    
    if coins[4] >= C:
        return "no exchange"
    
    for i in range(5, 10):
        while coins[i] > 0 and coins[4] < C:
            coins[i] -= 1
            coins[4] += 5
            coins[5] += 1
    
    if coins[4] >= C:
        return coins[4]
    else:
        return "can't exchange"
C, Y = map(int, input().split())
print(exchange(C, Y))