#include <algorithm>
#include <vector>

long long maxDoubleSliceSum(const std::vector<int>& a)
{
    int size = static_cast<int>(a.size());
    if (size < 3) {
        return 0;
    }

    std::vector<long long> p1(size, 0);
    std::vector<long long> p2(size, 0);

    for (int i = 2; i < size - 1; ++i) {
        p1[i] = std::max<long long>(0, p1[i - 1] + a[i - 1]);
        p2[size - i - 1] = std::max<long long>(0, p2[size - i] + a[size - i]);
    }

    long long sum = p1[1] + p2[1];
    for (int i = 1; i < size - 1; ++i) {
        sum = std::max(sum, p1[i] + p2[i]);
    }

    return sum;
}