A, B = list(map(int, input().split()))



for i in range(1, 10**5):

    if int(i * 0.08) == A and int(i * 0.1) == B:

        print(i)

        exit()



print((-1))
A, B = list(map(int, input().split()))



for i in range(100000):

    if (i * 8) // 100 == A and (i * 10) // 100 == B:

        print(i)

        exit()



print((-1))

A, B = list(map(int, input().split()))
for i in range(1, 10**5):
    if int(i * 0.08) == A and int(i * 0.1) == B:
        print(i)
        exit()
print((-1))

A, B = list(map(int, input().split()))
for i in range(100000):
    if (i * 8) // 100 == A and (i * 10) // 100 == B:
        print(i)
        exit()
print((-1))

-for i in range(1, 10**5): -    if int(i * 0.08) == A and int(i * 0.1) == B: +for i in range(100000): +    if (i * 8) // 100 == A and (i * 10) // 100 == B: