#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <functional>
#include <set>
#include <map>
using namespace std;
typedef long long int ll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef pair<ll, ll> pll;
typedef vector<pll> vpll;
typedef vector<vpll> vvpll;
#define rep(i, a, b) for (ll i = a; i < b; i++)
#define rev_rep(i, a, b) for (ll i = a; i >= b; i--)
#define sz(a) (ll) a.size()
#define mp(a, b) make_pair(a, b)
#define pb(a) push_back(a)
#define trav(itr, a, t) for (t::iterator itr = a.begin(); itr != a.end(); itr++)
const ll MAXM = 300LL;
const ll MAXB = MAXM * (2 * MAXM + 1LL);
const ll INF = 1'000'000'000'000'000'000LL;
ll M, L;
vll A;
vll in_greedy;
void reduce(vll& res, ll x, ll multiplier = 1) {
res.clear();
while (x) {
res.pb(multiplier);
x--;
if (x & 1LL) {
res.pb(multiplier);
x--;
}
x >>= 1LL;
multiplier *= 2LL;
}
}
int main() {
cin.tie(NULL)->sync_with_stdio(false);
cin >> M >> L;
A.resize(2 * M + 1);
rep(i, 0, 2 * M + 1) cin >> A[i];
ll s = 0LL;
rep(i, -M, M + 1) {
s += A[i + M] * i;
}
if (s < L) { // reverse the problem
rep(i, 1, M + 1) swap(A[M - i], A[M + i]);
L *= -1;
}
// greedy
in_greedy.resize(M + 1, 0);
s = 0LL;
ll n = 0LL;
rep(i, -M, 1) {
s += A[i + M] * i;
n += A[i + M];
}
rep(i, 1, M + 1) {
in_greedy[i] = max<ll>(0LL, min<ll>((L - s) / i, A[i + M]));
s += in_greedy[i] * i;
n += in_greedy[i];
}
// dp
ll dp[2 * MAXB + 1];
rep(i, 0, 2 * MAXB + 1) dp[i] = -INF;
if ((L - s >= -MAXB) && (L - s <= MAXB)) dp[MAXB + (L - s)] = n; // base case
vll deltas;
rep(w, 1, M + 1) {
// add w
reduce(deltas, min<ll>(2 * M, A[w + M] - in_greedy[w]));
trav(delta, deltas, vll) {
rep(i, - MAXB, MAXB + 1 - (*delta) * w) {
dp[i + MAXB] = max<ll>(dp[i + MAXB], dp[i + MAXB + (*delta) * w] + (*delta));
}
}
// remove w
reduce(deltas, min<ll>(2 * M, in_greedy[w]), -1);
trav(delta, deltas, vll) {
rev_rep(i, MAXB, - MAXB - (*delta) * w) {
dp[i + MAXB] = max<ll>(dp[i + MAXB], dp[i + MAXB + (*delta) * w] + (*delta));
}
}
}
if (dp[MAXB] < 0) {
cout << "impossible" << endl;
} else {
cout << dp[MAXB] << endl;
}
return 0;
}
