#include <bits/stdc++.h>
using namespace std;
#define REP(i, j, k) for (int i = j; i < k; i++)
#define RREP(i, j, k) for (int i = j; i >= k; i--)
template <class T>
inline bool mnto(T &a, const T b) {return a > b ? a = b, 1 : 0;}
template <class T>
inline bool mxto(T &a, const T b) {return a < b ? a = b, 1 : 0;}
typedef long long ll;
#define FI first
#define SE second
typedef pair<int, int> ii;
typedef pair<ll, ll> pll;
#define ALL(x) x.begin(), x.end()
#define SZ(x) (int) x.size()
#define pb push_back
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<ll> vll;
typedef tuple<int, int, int> iii;
#ifndef DEBUG
#define cerr if (0) cerr
#endif
const int MAXN = 305;
const int INF = 1000000005;
const ll LINF = 1000000000000000005;
const int MOD = 1000000007;
int m;
ll l;
ll a[MAXN * 2];
ll ans;
struct item {
int v;
ll a;
int c;
};
vector<item> items;
ll getitems() {
ll tot = 0;
REP (i, -m, m + 1) {
if (i <= 0) {
tot += a[i + MAXN] * i;
ans += a[i + MAXN];
if (i != 0) {
items.pb({-i, a[i + MAXN], -1});
}
} else {
ll dif = l - tot;
ll take = min(a[i + MAXN], dif / i);
tot += take * i;
ans += take;
if (take > 0) {
items.pb({-i, take, -1});
}
if (a[i + MAXN] - take > 0) {
items.pb({i, a[i + MAXN] - take, 1});
}
}
}
return tot;
}
int main() {
#ifndef DEBUG
ios::sync_with_stdio(0), cin.tie(0);
#endif
cin >> m >> l;
REP (i, -m, m + 1) {
cin >> a[i + MAXN];
}
if (l < 0) {
l *= -1;
reverse(a + MAXN - m, a + MAXN + m + 1);
}
ll tot = 0;
REP (i, 1, m + 1) {
tot += a[i + MAXN] * i;
}
if (tot < l) {
cout << "impossible\n";
return 0;
}
tot = getitems();
ll rem = l - tot;
if (rem > m) {
l *= -1;
reverse(a + MAXN - m, a + MAXN + m + 1);
ans = 0;
items.clear();
tot = getitems();
rem = l - tot;
}
cerr << ans << ' ' << tot << '\n';
assert(rem <= m);
int sz = m * m;
vll dp(sz * 2 + 5, -LINF);
dp[sz] = 0;
for (auto [v, a, c] : items) {
for (ll k = 0; abs(k) < abs(v); k += v / abs(v)) {
int ptr = 0;
deque<pll> dq;
for (ll j = (v < 0 ? sz : -sz) + k; j <= sz && j >= -sz; j += v) {
while (!dq.empty() && ptr - dq.front().SE > a) {
dq.pop_front();
}
if (dp[j + sz] != -LINF) {
while (!dq.empty() && dq.back().FI - dq.back().SE * c <=
dp[j + sz] - ptr * c) {
dq.pop_back();
}
dq.pb({dp[j + sz], ptr});
}
if (dq.empty()) {
dp[j + sz] = -LINF;
} else {
dp[j + sz] = dq.front().FI + ptr * c - dq.front().SE * c;
}
ptr++;
cerr << j << ' ' << dp[j + sz] << '\n';
}
}
}
if (dp[rem + sz] == -LINF) {
cout << "impossible\n";
} else {
cout << ans + dp[rem + sz] << '\n';
}
return 0;
}
