#include<bits/stdc++.h>
using namespace std;
#define ll long long
int const M = 350;
int const MM = M*M;
int const off = 340;
int const off2 = off*off;
ll A[2*M];
ll dp[2][2*MM];
int m; ll l;
int main() {
cin >> m >> l;
for (int i = -m; i <= m; ++i) cin >> A[i+off];
ll zz = -l;
for (int i = -m; i <= m; ++i) {
zz += A[i+off] * i;
}
if (zz < 0) {
l = -l;
for (int i = -m; i < 0; ++i) {
int j = -i;
int idx = i+off, idx2 = j+off;
swap(A[idx], A[idx2]);
}
}
ll itm = 0;
memset(dp, 0xc3, sizeof dp);
dp[0][off2] = 0;
int idp = 1;
for (int i = -m; i <= m; ++i) {
ll take = i <= 0 ? A[i+off] : min(A[i+off], max(0LL, l / i));
l -= take * i;
A[i+off] -= take;
itm += take;
memcpy(dp[idp], dp[idp^1], sizeof dp[idp]);
if (i != 0) {
// try_add_to_dp A[i+off]
for (int j = -m*m; j < -m*m+i; ++j) {
deque<int> dq;
dq.emplace_back(j);
for (int k = j + i; k <= m*m; k += i) {
while (dq.size() && (k-dq.front())/i > A[i+off]) dq.pop_front();
while (dq.size() && dp[idp^1][k+off2] >= dp[idp^1][dq.back()+off2]+(k-dq.back())/i) dq.pop_back();
dq.emplace_back(k);
if (dq.size()) dp[idp][k+off2] = max(dp[idp][k+off2],
dp[idp^1][dq.front()+off2] + (k-dq.front())/i);
}
//for (int k = 1; (k <= A[i+off]) && (j-k*i>=-m*m) && (j-k*i<=m*m); ++k) {
// dp[idp][j+off2] = max(dp[idp][j+off2], dp[idp^1][j-k*i+off2] + k);
//}
}
memcpy(dp[idp^1], dp[idp], sizeof dp[idp]);
// try_delete_from_dp take
if (i > 0) {
for (int j = m*m; j >= -m*m; --j) {
deque<int> dq;
dq.emplace_back(j);
for (int k = j-i; k >= -m*m; k -= i) {
while (dq.size() && (dq.front()-k)/i > take) dq.pop_front();
while (dq.size() && dp[idp^1][k+off2] >= dp[idp^1][dq.back()+off2]-(dq.back()-k)/i)
dq.pop_back();
dq.emplace_back(k);
if (dq.size()) dp[idp][k+off2] = max(dp[idp][k+off2],
dp[idp^1][dq.front()+off2] - (dq.front()-k)/i);
}
//for (int k = 1; (k <= take) && (j+k*i>=-m*m) && (j+k*i<=m*m); ++k) {
// dp[idp][j+off2] = max(dp[idp][j+off2], dp[idp^1][j+k*i+off2] - k);
//}
}
}
else {
for (int j = -m*m; j < -m*m+i; ++j) {
deque<int> dq;
dq.emplace_back(j);
for (int k = j + i; k <= m*m; k += i) {
while (dq.size() && (dq.front()-k)/i > take) dq.pop_front();
while (dq.size() && dp[idp^1][k+off2] >= dp[idp^1][dq.back()+off2]-(dq.back()-k)/i)
dq.pop_back();
dq.emplace_back(k);
if (dq.size()) dp[idp][k+off2] = max(dp[idp][k+off2],
dp[idp^1][dq.front()+off2] - (dq.front()-k)/i);
}
}
}
}
idp ^= 1;
}
idp ^= 1;
if (l < -m*m || l > m*m || dp[idp][l+off2] < -1e9) {
cout << "impossible\n";
}
else {
cout << (dp[idp][l+off2] + itm) << '\n';
}
}
