#include <bits/stdc++.h>
int main() {
int m;
int64_t l;
std::cin >> m >> l;
std::vector<std::pair<int64_t, int>> a;
int64_t high = 0, low = 0;
for (int64_t i = -m; i <= m; ++i) {
uint64_t x;
std::cin >> x;
if (i > 0) {
high += x * i;
} else {
low += x * i;
}
while (x > 0) {
int w = std::bit_width(x) - 1;
if (std::has_single_bit(x + 1)) {
w += 1;
}
for (int bt = 0; bt < w; ++bt) {
a.push_back({i << bt, 1LL << bt});
}
x -= (1LL << w) - 1;
}
}
if (l < low or l > high) {
std::cout << "impossible\n";
return 0;
}
const int inf = 1e9;
std::vector dp(2, std::vector<int>(high - low + 1, -inf));
dp[0][-low] = 0;
for (int i = 1; i <= a.size(); ++i) {
for (int j = low; j <= high; ++j) {
dp[i & 1][j - low] = dp[!(i & 1)][j - low];
if (low <= j - a[i - 1].first and j - a[i - 1].first <= high) {
dp[i & 1][j - low] = std::max(dp[i & 1][j - low], dp[!(i & 1)][j - a[i - 1].first - low] + a[i - 1].second);
}
}
}
int ans = dp[a.size() & 1][l - low];
if (ans < 0) {
std::cout << "impossible\n";
} else {
std::cout << ans << '\n';
}
}
