# C - Tax Increase

from math import floor



def calc(a: int, b: int) -> int:

    for i in range(1, 10001):

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

            return i

    return -1





def main():

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

    print((calc(A, B)))





if __name__ == "__main__":

    main()

# C - Tax Increase

from math import floor





def calc(a: int, b: int) -> int:

    for i in range(1, 1010):

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

            return i

    return -1





def main():

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

    print((calc(A, B)))





if __name__ == "__main__":

    main()

# C - Tax Increase
from math import floor


def calc(a: int, b: int) -> int:
    for i in range(1, 10001):
        if floor(i * 0.08) == a and floor(i * 0.1) == b:
            return i
    return -1


def main():
    A, B = list(map(int, input().split()))
    print((calc(A, B)))


if __name__ == "__main__":
    main()

# C - Tax Increase
from math import floor


def calc(a: int, b: int) -> int:
    for i in range(1, 1010):
        if floor(i * 0.08) == a and floor(i * 0.1) == b:
            return i
    return -1


def main():
    A, B = list(map(int, input().split()))
    print((calc(A, B)))


if __name__ == "__main__":
    main()

-    for i in range(1, 10001): +    for i in range(1, 1010):