#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define ld double
#define ll long long
mt19937 rnd(51);
const int INF = 1e9, M = 5.1e5 + 10, N = 1e3 + 10;
vector<int> calc_dp(vector<pair<int, ll>> u, bool f, int n) {
vector<int> dp(n);
vector<pair<ll, ll>> upd;
for (int i = 0; i < u.size(); i++) {
ll t = 0;
while ((1LL << (t + 1)) <= u[i].second) {
t++;
}
for (int j = 0; j < t; j++) {
upd.pb({u[i].first * (1LL << j), (1LL << j)});
}
upd.pb({u[i].first * (u[i].second - (1LL << t) + 1), (u[i].second - (1LL << t) + 1)});
}
if (f) {
for (int i = 1; i < n; i++) dp[i] = -INF;
} else {
for (int i = 1; i < n; i++) dp[i] = INF;
}
for (auto to : upd) {
if (to.first >= n) continue;
if (f) {
for (int j = n - to.first - 1; j >= 0; j--) {
if (dp[j] != -INF) {
dp[j + to.first] = max(dp[j + to.first], dp[j] + (int)to.second);
}
}
} else {
for (int j = n - to.first - 1; j >= 0; j--) {
if (dp[j] != INF) {
dp[j + to.first] = min(dp[j + to.first], dp[j] + (int)to.second);
}
}
}
}
return dp;
}
ll solve_pos(ll m, ll L, vector<ll> pos, int need_const) {
if (L < 0) {
return -1;
}
ll sum = L, cnt = 0;
vector<pair<int, ll>> u1, u2;
for (ll i = 1; i <= m; i++) {
if (i * pos[i] > sum) {
ll can = sum / i;
sum -= can * i;
cnt += can;
u1.pb({i, can});
u2.pb({i, pos[i] - can});
for (int j = i + 1; j <= m; j++) {
u2.pb({j, pos[j]});
}
break;
} else {
sum -= i * pos[i];
cnt += pos[i];
u1.pb({i, pos[i]});
}
}
if (sum == 0) {
return cnt;
} else {
vector<int> dp1 = calc_dp(u1, 0, need_const), dp2 = calc_dp(u2, 1, need_const);
ll mx = -1;
for (int j = 0; j + sum < need_const; j++) {
if (dp2[j + sum] >= 0 && dp1[j] != INF) {
mx = max(mx, cnt + dp2[j + sum] - dp1[j]);
}
}
return mx;
}
}
ll solve_any(ll m, ll L, vector<ll> neg, vector<ll> pos) {
ll sum_neg = 0, sum_pos = 0;
vector<pair<int, ll>> u1, u2;
for (int i = 1; i <= m; i++) {
u1.pb({i, neg[i]});
sum_neg += i * neg[i];
}
for (int i = 1; i <= m; i++) {
u2.pb({i, pos[i]});
sum_pos += i * pos[i];
}
if (L > sum_pos) return -1;
vector<int> dp1 = calc_dp(u1, 1, M), dp2 = calc_dp(u2, 1, M);
ll mx = -1;
ll need_val = min(sum_neg, sum_pos - L);
for (int j = -100; j <= 100; j++) {
ll res = solve_pos(m, j + need_val, neg, N);
ll res2 = solve_pos(m, L + (j + need_val), pos, N);
if (res != -1 && res2 != -1) {
mx = max(mx, res + res2);
}
}
return mx;
}
signed main() {
#ifdef LOCAL
freopen("input.txt", "r", stdin);
#endif // LOCAL
ios_base::sync_with_stdio(0);
cin.tie(0);
ll m, L;
cin >> m >> L;
ll zero = 0;
vector<ll> neg, pos{0};
for (int i = 0; i < 2 * m + 1; i++) {
ll a;
cin >> a;
if (i < m) {
neg.pb(a);
} else if (i == m) {
zero += a;
} else {
pos.pb(a);
}
}
neg.pb(0);
reverse(neg.begin(), neg.end());
ll mx = 0;
for (auto to : neg) {
mx = max(mx, to);
}
ll res;
if (mx == 0) {
res = solve_pos(m, L, pos, M);
} else {
if (L < 0) {
L = abs(L);
swap(neg, pos);
}
res = solve_any(m, L, neg, pos);
}
if (res == -1) {
cout << "impossible" << endl;
} else {
cout << zero + res << endl;
}
return 0;
}
