#include <bits/stdc++.h>
using namespace std;
using ll = long long;
unordered_map<int, ll> take, not_take;
int N = 300 * 300;
const ll LINF = -2e18;
vector<ll> dp(2 * N + 1, LINF), ndp(2 * N + 1, LINF);
void add(ll v, ll d) {
ndp = dp;
for (int i = 0; i <= 2 * N; ++i) {
if (0 <= i - v * d && i - v * d <= 2 * N) {
dp[i] = max(dp[i], ndp[i - v * d] + v);
}
}
for (int i = 0; i <= 2 * N; ++i) {
dp[i] = (dp[i] <= LINF + N ? LINF : dp[i]);
}
}
void sub(ll v, ll d) {
ndp = dp;
for (int i = 0; i <= 2 * N; ++i) {
if (0 <= i + v * d && i + v * d <= 2 * N) {
dp[i] = max(dp[i], ndp[i + v * d] - v);
}
}
for (int i = 0; i <= 2 * N; ++i) {
dp[i] = (dp[i] <= LINF + N ? LINF : dp[i]);
}
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int m;
ll L;
cin >> m >> L;
ll res = 0;
for (int i = -m; i <= m; ++i) {
cin >> not_take[i];
}
if (L < 0) {
for (int i = -m; i <= 0; ++i) {
swap(not_take[i], not_take[-i]);
}
L = -L;
}
ll sum = 0;
for (int i = -m; i <= 0; ++i) {
ll now = not_take[i];
sum += now * i;
not_take[i] -= now;
take[i] += now;
res += now;
}
for (int i = 1; i <= m; ++i) {
ll now = min(not_take[i], (L - sum) / i);
sum += now * i;
not_take[i] -= now;
take[i] += now;
res += now;
}
if (L - sum > m * m) { // max take all i = m and m * m times?
for (int i = -m; i < 0; ++i) {
ll now = min(take[i], (L - sum) / (-i));
sum -= now * i;
take[i] -= now;
not_take[i] += now;
res -= now;
}
}
// assert(sum <= L);
for (int i = 0; i <= 2 * N; ++i) {
dp[i] = ndp[i] = LINF;
}
dp[N] = ndp[N] = 0;
for (int i = -m ; i <= m; ++i) {
if (i == 0) continue;
ll k, s;
s = 0;
k = min((ll)m, not_take[i]);
for (ll j = 0; s + (1 << j) <= k; s += (1 << j), ++j) {
add((1 << j), i);
}
add(k - s, i);
s = 0;
k = min((ll)m, take[i]);
for (ll j = 0; s + (1 << j) <= k; s += (1 << j), ++j) {
sub((1 << j), i);
}
sub(k - s, i);
}
ll offset = L - sum + N;
// cout << L << " " << sum << " " << N << endl;
assert(offset >= 0);
// assert(offset <= 2 * N);
if (offset > N * 2) {
cout << "impossible\n";
return 0;
}
if (dp[offset] == LINF) {
cout << "impossible\n";
return 0;
}
cout << res + dp[offset] << "\n";
}
