#include "bits/stdc++.h"
using namespace std;
#define int long long
const int MAXN = 3e5 + 10;
const int MOD = 1e9 + 7;
#define ll __int128
mt19937_64 rng((int)std::chrono::steady_clock::now().time_since_epoch().count());
int rnd(int x, int y) {
int u = uniform_int_distribution<int>(x, y)(rng); return u;
}
ll read() { int x; cin >> x; return (ll)x; }
long long bm(long long b, long long p) {
if(p==0) return 1 % MOD;
long long r = bm(b, p >> 1);
if(p&1) return (((r*r) % MOD) * b) % MOD;
return (r*r) % MOD;
}
long long inv(long long b) {
return bm(b, MOD-2);
}
long long f[MAXN];
long long nCr(int n, int r) {
long long ans = f[n]; ans *= inv(f[r]); ans %= MOD;
ans *= inv(f[n-r]); ans %= MOD; return ans;
}
long long fib[MAXN], lucas[MAXN];
void precomp() {
for(int i=0; i<MAXN; i++) f[i] = (i == 0 ? 1 % MOD : (f[i-1] * i) % MOD);
lucas[0] = 2;
lucas[1] = 1;
for(int i=2; i<MAXN; i++) lucas[i] = (lucas[i-2] + lucas[i-1]) % MOD;
fib[0] = 0;
fib[1] = 1;
for(int i=2; i<MAXN; i++) fib[i] = (fib[i-2] + fib[i-1]) % MOD;
}
int fastlog(int x) {
return (x == 0 ? -1 : 64 - __builtin_clzll(x) - 1);
}
void gay(int i) { cout << "Case #" << i << ": "; }
int csb(int l, int r, int k) { // count number of [l, r] such that i & 2^k > 0
if(l > r) return 0;
if(l == 0) {
int s = r / (1ll << (k+1)); // number of complete cycles
int t = r % (1ll << (k+1));
int ans = s * (1ll << k);
ans += (t >= (1ll << k) ? t - (1ll << k) + 1 : 0);
return ans;
}
else return csb(0, r, k) - csb(0, l - 1, k);
}
int lis(vector<int> a) {
int n = a.size();
int bucket[n+1];
for(int i=1; i<=n; i++) bucket[i] = 1e18;
int ans = 1;
for(int x: a) {
auto it = lower_bound(bucket + 1, bucket +n +1, x);
int d = distance(bucket, it);
ans = max(ans, d);
bucket[d] = min(bucket[d], x);
}
return ans;
}
vector<int> all_min_knapsacks(vector<int> v, int l, int r) {
int freq[601];
for(int i=0; i<=600; i++) freq[i] = 0;
for(int x: v) freq[x + 300]++;
unordered_map<int, int> dp[601];
for(int i=0; i<=600; i++) for(int j=l; j<=r; j++) dp[i][j] = 1e18;
for(int i=l; i<=0; i++) {
if(i % 300 == 0 && abs(i / 300) <= freq[0]) {
dp[0][i] = abs(i/300);
}
}
for(int i=1; i<=600; i++) {
for(int j=l; j<=r; j++) {
dp[i][j] = dp[i-1][j];
for(int k=1; k<=freq[i]; k++) {
int res = j - k * (i - 300);
if(l <= res && res <= r) dp[i][j] = min(dp[i][j], dp[i-1][res] + k);
}
}
}
vector<int> vt;
for(int i=l; i<=r; i++) {
if(dp[600][i] > 1e16) vt.push_back(-1);
else vt.push_back(dp[600][i]);
}
return vt;
}
vector<int> all_max_knapsacks(vector<int> v, int l, int r) {
int freq[601];
for(int i=0; i<=600; i++) freq[i] = 0;
for(int x: v) freq[x + 300]++;
unordered_map<int, int> dp[601];
for(int i=0; i<=600; i++) for(int j=l; j<=r; j++) dp[i][j] = -1e18;
for(int i=l; i<=0; i++) {
if(i % 300 == 0 && abs(i / 300) <= freq[0]) {
dp[0][i] = abs(i/300);
}
}
for(int i=1; i<=600; i++) {
for(int j=l; j<=r; j++) {
dp[i][j] = dp[i-1][j];
for(int k=1; k<=freq[i]; k++) {
int res = j - k * (i - 300);
if(l <= res && res <= r) dp[i][j] = max(dp[i][j], dp[i-1][res] + k);
}
}
}
vector<int> vt;
for(int i=l; i<=r; i++) {
if(dp[600][i] < -1e16) vt.push_back(-1);
else vt.push_back(dp[600][i]);
}
return vt;
}
void solve(int tc) {
int m, l; cin >> m >> l;
unordered_map<int, int> a;
for(int i=-m; i<=m; i++) cin >> a[i];
if(l < 0) {
for(int i=-m; i<0; i++) swap(a[i], a[-i]);
l = -l;
}
int cnt = a[0], sum = 0;
for(int i=1; i<=m; i++) {
int owo = (a[i] - a[-i]) * i;
cnt += a[i] + a[-i];
sum += owo;
}
if(sum == l) {
cout << cnt << "\n"; return;
}
unordered_map<int, int> chosen;
for(int i=-m; i<=m; i++) chosen[i] = a[i];
if(sum < l) {
for(int i=-m; i<0; i++) {
int rem = (l - sum) / (-i);
rem = min(rem, a[i]);
if(sum - rem * i == l) {
chosen[i] -= rem;
sum -= rem * i;
break;
}
if(rem == a[i]) {
chosen[i] = 0;
sum -= rem * i;
}
else {
rem++;
chosen[i] -= rem;
sum -= rem * i;
break;
}
}
if(sum < l) {
cout << "impossible\n"; return;
}
}
else {
for(int i=m; i>0; i--) {
int rem = (sum - l) / i;
rem = min(rem, a[i]);
chosen[i] -= rem;
sum -= rem * i;
}
}
if(sum == l) {
int sm = 0;
for(int i=-m; i<=m; i++) sm += chosen[i];
cout << sm << "\n";
return;
}
vector<int> in, out;
for(int i=-m; i<=m; i++) {
for(int j=0; j<min(m, chosen[i]); j++) in.push_back(i);
for(int j=0; j<min(m, a[i] - chosen[i]); j++) out.push_back(i);
}
if(in.empty() || out.empty()) {
cout << "impossible\n"; return;
}
int A = sum - l;
vector<int> resin = all_min_knapsacks(in, -m*m, m*m);
vector<int> resout = all_max_knapsacks(out, -m*m, m*m);
int sm = 0;
for(int i=-m; i<=m; i++) sm += chosen[i];
int ans = -1;
int id;
for(int x=0; x<resout.size(); x++) {
if(resout[x] != -1 && A + x < resin.size() && resin[A + x] != -1) {
if(sm - resin[A + x] + resout[x] > ans) {
ans = sm - resin[A + x] + resout[x];
id = x;
}
}
}
cout << (ans == -1 ? "impossible" : to_string(ans)) << "\n";
}
int32_t main() {
precomp();
ios::sync_with_stdio(0); cin.tie(0);
int t = 1; //cin >> t;
for(int i=1; i<=t; i++) solve(i);
}
// I don't know geometry.
// Teaming is unfair.
/*
5 16
0 0 0 0 0 0 0 0 3 2 1
*/
