C,Y = map(int, input().split())
if C*100>Y:
    print('can\'t exchange')
elif C<=(Y//100)%5:
    print('no exchange')
else:
    if (Y//100)%5>=C%5:
        print((C//5)*5+(Y//100)%5)
    else:
        print(-(-C//5)*5+(Y//100)%5)