/*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;
for (int v = M; v >= 1; v--)
{
if (A[v] > 0 && A[-v] > 0)
{
ll x = min(A[v] - 1, A[-v] - 1);
int t = 0;
int d = 0;
if (A[v] > A[-v])
t = 1;
if (A[-v] > A[v])
d = 1;
L -= t * v;
L += d * v;
A[v] -= x + t;
A[-v] -= x + d;
pl += 2 * x + t + d;
}
// while (A[v] > 0 && A[-v] > 0)
// {
// if (abs(L) < v && A[v] > 0 && A[-v] > 0)
// {
// ll x = min(A[v] - 1, A[-v] - 1);
// A[v] -= x + 1;
// A[-v] -= x;
// pl += 2 * x + 1;
// continue;
// }
// if (L > 0)
// {
// ll k = min(A[v], max(1ll, L / v));
// A[v] -= k;
// L -= v * k;
// pl += k;
// }
// else
// {
// ll k = min(A[-v], max(1ll, L / v));
// A[-v] -= k;
// L += v * k;
// pl += k;
// }
//}
}
L = -L;
ll cnt = 0;
for (int l = -M; l <= M; l++)
{
L += l * A[l];
cnt += A[l];
}
map<ll, ll>D;
D[0] = 0;
ll del = 30;
vector<int>gal;
for (int i = -M; i <= M; i++)
{
if (i != 0)
gal.push_back(i);
}
for (int v = M; v >= 1; v--)
for (int l : {v, -v})
{
if (l == 0)
continue;
map<ll, ll>D_;
for (pair<ll, ll>v : D)
{
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]);
for (ll c = lo; c <= hi; c++)
{
ll v_ = v.first + l * c;
ll c_ = v.second + c;
if (D_.count(v_) == 0)
D_[v_] = c_;
else
D_[v_] = min(D_[v_], c_);
}
}
D = D_;
}
if (D.count(L))
cout << pl + cnt - D[L] << "\n";
else
cout << "impossible\n";
}
