C, Y = map(int, input().split())

A = []
for i in range(4):
    A.append(10**i)
    if i+1 < 4:
        A.append(10**i*5)
A.append(10**3*2)
A.append(10**3*5)
A.append(10**4)

cnt = [0]*10
for i in reversed(range(10)):
    cnt[i] = Y//A[i]
    Y %= A[i]

if cnt[4] >= C:
    print("no exchange")
else:
    r = C-cnt[4]
    c = 0
    for i in range(5, 10):
        c += A[i]//100*cnt[i]
    if cnt[4]+c >= C:
        a = (r+5-1)//5
        print(a*5+cnt[4])
    else:
        print("can't exchange")