python 3.4.2

__author__ = 'alexta'


def sort(a, sample):
    k = 1
    key_left = key_right = 0

    while k < len(a):
        for i in range(k):
            if (a[i] == sample):
                key_left += 1

        for j in range(k, len(a)):
            if (a[j] != sample):
                key_right += 1

        if (key_left == key_right):
            return k

        key_left = key_right = 0
        k += 1

    return -1


def main():
    sample = 5
    a = [5, 5, 1, 7, 2, 3, 5]

    try:
        print(sort(a, sample))
    except ValueError:
        return -1


if __name__ == '__main__':
    main()