long summingPieces(vector<long> A) {
    long mod = 1000000007;
    vector<long> twoPower = { 1 };
    for (int i = 1; i <= A.size(); i++) twoPower.push_back((2 * twoPower.back()) % mod);
    vector<vector<long>> storage = {{A[0], A[0], A[0]}};
    long L = A[0], N, P, Q;
    for (int i = 1; i < A.size(); i++) {
        P = (storage[i-1][1] + twoPower[i] * A[i]) % mod;
        Q = (storage[i-1][2] + storage[i-1][1] + (twoPower[i+1] - 1) * A[i]) % mod;
        N = (L + Q) % mod;
        L = (L + N) % mod;
        storage.push_back({N, P, Q});
    }
    return storage.back()[0];
}