/*input
2 5
2 3 1 1 4
*/
#pragma GCC optimize ("O3")
#pragma GCC target("avx,avx2,fma")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
template <typename T>
using oset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
mt19937_64 rng(0);
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int M;
ll L;
cin >> M >> L;
ll A_[2 * M + 1];
ll* A = A_ + M;
for (int i = -M; i <= M; i++)
cin >> A[i];
ll pl = 0;
pl += A[0];
A[0] = 0;
L = -L;
ll cnt = 0;
for (int l = -M; l <= M; l++)
{
L += l * A[l];
cnt += A[l];
}
cc_hash_table<ll, ll>D;
D[0] = 0;
ll del = M;
cc_hash_table<ll, int>X[M + 1];
X[0][0] = 0;
int mxe = 50;
for (int v = 1; v <= M; v++)
{
for (pair<ll, int>a : X[v - 1])
{
int mxe1 = mxe - a.second;
for (int l : {v, -v})
{
for (int i = 0; i <= mxe1 && i <= A[l]; i++)
{
ll val = a.first + i * l;
int ej = a.second + i;
auto it = X[v].find(val);
if (it == X[v].end())
X[v][val] = ej;
else
it->second = min(it->second, ej);
}
}
}
}
if (X[M].find(L) != X[M].end())
{
cout << pl + cnt - X[M][L] << "\n";
return 0;
}
ll infi = 5e18;
ll best = infi;
A[0] = 1;
for (int v = M; v >= 1; v--)
for (int l : {v, -v})
{
if (l == 0)
continue;
cc_hash_table<ll, ll>D_;
for (pair<ll, ll>v : D)
{
if (v.second >= best)
continue;
ll k = (L - v.first) / l;
k = max(k, 0ll);
k = min(k, A[l]);
ll lo = max(0ll, k - del);
ll hi = min(k + del, A[l]);
if (abs(L - (v.first + k * l)) < abs(l) && A[L - (v.first + k * l)] > 0)
{
int d = 1;
if (L - (v.first + k * l) == 0)
d = 0;
ll c_ = v.second + k + d;
best = min(best, c_);
}
else
{
for (ll c = lo; c <= hi; c++)
{
ll v_ = v.first + l * c;
ll c_ = v.second + c;
if (c_ >= best)
continue;
auto it1 = X[abs(l) - 1].find(L - v_);
if (it1 != X[abs(l) - 1].end())
{
best = min(best, c_ + it1->second);
}
else {
auto it = D_.find(v_);
if (it == D_.end())
D_[v_] = c_;
else
it->second = min(it->second, c_);
}
}
}
}
D = D_;
}
if (best < infi)
cout << pl + cnt - best << "\n";
else
cout << "impossible\n";
}
