def solution(A):
    sums = []

    curr_sum = 0
    for i in A:
        curr_sum += i
        sums.append(curr_sum)

    for i in xrange(0, len(A)):
        left_sum = 0 if i == 0 else sums[i-1]
        right_sum = 0 if i == len(A) else sums[-1] - sums[i]

        if right_sum == left_sum:
            return i

    return -1


a = [-1, 3, -4, 5, 1, -6, 2, 1]
print solution(a)