#include <bits/stdc++.h>
using ll = long long;
using std::vector;
using std::pair;
using std::deque;
constexpr int inf = std::numeric_limits<int>::max() / 2;
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
int M;
ll T;
std::cin >> M >> T;
vector<ll> A(2 * M + 1);
ll S = 0;
for (int i = -M; i <= M; ++i) {
std::cin >> A[i + M];
S += i * A[i + M];
}
if (S < T) {
T = -T;
std::reverse(A.begin(), A.end());
}
const int N = M * M;
vector<int> dp(2 * N + 1, -inf);
dp[N] = 0;
const auto update_positive = [&](const ll K, const int W, const int V) {
for (int r = 0; r < W; ++r) {
if (r >= (int)dp.size()) {
break;
}
deque<pair<int, int>> deq;
for (int q = 0;; ++q) {
const int i = q * W + r;
if (i >= (int)dp.size()) {
break;
}
const int add = dp[i] - q * V;
while (!deq.empty() and deq.back().first < add) {
deq.pop_back();
}
deq.emplace_back(add, q);
while (deq.front().second + K < q) {
deq.pop_front();
}
dp[i] = std::max(dp[i], deq.front().first + q * V);
}
}
};
const auto update = [&](const ll K, const int W, const int V) {
if (W > 0) {
update_positive(K, W, V);
}
if (W < 0) {
std::reverse(dp.begin(), dp.end());
update_positive(K, -W, V);
std::reverse(dp.begin(), dp.end());
}
};
S = 0;
ll sum = 0;
for (int i = -M; i <= M; ++i) {
const ll take = i <= 0 ? A[i + M] : std::clamp<ll>((T - S) / i, 0, A[i + M]);
const ll remain = A[i + M] - take;
S += i * take;
sum += take;
update(take, -i, -1);
update(remain, i, 1);
}
if (std::abs(T - S) > N or dp[T - S + N] < -2 * M) {
std::cout << "impossible\n";
} else {
std::cout << sum + dp[T - S + N] << '\n';
}
return 0;
}
