C, Y = map(int, input().split())
if 100 * C > Y:
    print("can't exchange")
    exit()
    
Y %= 500
c = Y // 100
if c >= C:
    print("no exchange")
    exit()
    
for i in range(C//5*5, C//5*5 + 100):
    if i >= C and i % 5 == c:
        print(i)
        exit()