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

for i in range(500000):

    if int(i * 0.08) == A and int(i*0.10) == B:

        print(i)

        exit()

print((-1))

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

for i in range(100000):

    if int(i*0.08) == A and int(i*0.10) == B:

        print(i)

        exit()

print((-1))

A, B = list(map(int, input().split()))
for i in range(500000):
    if int(i * 0.08) == A and int(i * 0.10) == B:
        print(i)
        exit()
print((-1))

A, B = list(map(int, input().split()))
for i in range(100000):
    if int(i * 0.08) == A and int(i * 0.10) == B:
        print(i)
        exit()
print((-1))

-for i in range(500000): +for i in range(100000):