from math import floor



def main():

    a, b = list(map(int, input().split()))

    

    ans = -1

    for i in range(10000):

        if floor(i * 0.08) == a and floor(i * 0.1) == b:

            ans = i

            break

    print(ans)



if __name__ == "__main__":

    main()
from math import floor



def main():

    a, b = list(map(int, input().split()))

    

    ans = -1

    for i in range(1, 1001):

        if floor(i * 0.08) == a and floor(i * 0.1) == b:

            ans = i

            break

    print(ans)



if __name__ == "__main__":

    main()
from math import floor


def main():
    a, b = list(map(int, input().split()))
    ans = -1
    for i in range(10000):
        if floor(i * 0.08) == a and floor(i * 0.1) == b:
            ans = i
            break
    print(ans)


if __name__ == "__main__":
    main()

from math import floor


def main():
    a, b = list(map(int, input().split()))
    ans = -1
    for i in range(1, 1001):
        if floor(i * 0.08) == a and floor(i * 0.1) == b:
            ans = i
            break
    print(ans)


if __name__ == "__main__":
    main()

-    for i in range(10000): +    for i in range(1, 1001):