#include <bits/stdc++.h>
using namespace std;
using namespace std::chrono;
#define DEBUG(x) cerr << #x << " = " << x << endl;
using ll = long long;
const int MXM = 305;
const ll C = 1e5;
const ll INF = 1e18;
ll m, l;
ll A[2*MXM+1];
ll cnt[2*MXM+1];
ll dp[2*C+1];
string my_ans;
void solve(istream& is, ostream &os)
{
my_ans = "";
memset(A, 0, sizeof(A));
memset(cnt, 0, sizeof(cnt));
memset(dp, 0, sizeof(dp));
is >> m >> l;
ll neg = 0, zeroes = 0;
for(ll i = 0; i < 2*m+1; i++) {
ll val = i-m;
is >> A[i];
if(val < 0) {
neg += val*A[i];
}
else if(val == 0) {
zeroes = A[i];
}
}
// if(neg) {
// cerr << "Not all positive\n";
// return;
// }
// else {
// cerr << "All positive\n";
// }
ll init_take = 0;
ll curr = 0;
// positive greedy take
for(ll i = m+1; i < 2*m+1; i++) {
ll val = i-m;
ll left = l-curr-neg;
ll take = min((left+val-1)/val, A[i]);
cnt[i] += take;
curr += val*take;
init_take += take;
// if(take) {
// cerr << val << ": " << take << "\n";
// }
}
// negative greedy take
for(ll i = m-1; i >= 0; i--) {
ll val = i-m, abs_val = labs(val);
ll left = curr-l;
ll take = min(left/abs_val, A[i]);
cnt[i] += take;
curr += val*take;
init_take += take;
// if(take) {
// cerr << val << ": " << take << "\n";
// }
}
DEBUG(curr);
fill(dp, dp+2*C+1, -INF);
dp[C] = init_take;
for(ll i = 0; i < 2*m+1; i++) {
ll val = i-m, abs_val = labs(val);
if(val == 0) continue;
// subtract used
ll sub = min((2*C+1+abs_val-1)/abs_val, cnt[i]);
// add unused
ll add = min((2*C+1+abs_val-1)/abs_val, A[i]-cnt[i]);
// if(sub || add) {
// cerr << val << ":\n";
// cerr << sub << " " << add << "\n";
// }
int sign = 1;
if(val < 0) {
swap(sub, add);
sign = -1;
}
for(ll k = 0; k < 40 && sub > 0; k++) {
ll w = 1LL << k;
int times = (w & sub) ? 1 : 2;
sub -= times*w;
for(int t = 0; t < times; t++)
for(ll j = w*abs_val; j < 2*C+1; j++) {
dp[j-w*abs_val] = max(dp[j-w*abs_val], dp[j]-w*sign);
}
}
for(ll k = 0; k < 40 && add > 0; k++) {
ll w = 1LL << k;
int times = (w & add) ? 1 : 2;
add -= times*w;
for(int t = 0; t < times; t++)
for(ll j = 2*C-w*abs_val; j >= 0; j--) {
dp[j+w*abs_val] = max(dp[j+w*abs_val], dp[j]+w*sign);
}
}
}
ll look_for = C+l-curr;
DEBUG(look_for);
if(look_for < 0 || look_for >= 2*C+1 || dp[look_for] < 0) {
cout << "impossible";
my_ans = "impossible";
}
else {
cout << dp[look_for]+zeroes;
my_ans = to_string(dp[look_for]+zeroes);
}
cout << "\n";
}
int main()
{
bool manual;
//cout << "manual (1, 0): "; cin >> manual;
manual = true;
if(manual) {
solve(cin, cout);
}
else {
const int TESTS = 62;
for(int t = 1; t <= TESTS; t++) {
auto stop = steady_clock::now();
string input_file = "tests/" + to_string(t) + ".in";
string output_file = "tests/" + to_string(t) + ".out";
ifstream in(input_file);
ifstream out(output_file);
cerr << input_file << ":\n";
solve(in, cout);
if(my_ans != "") {
cerr << "answers: ";
string ans; getline(out, ans);
cout << my_ans << ", expected = " << ans << "\n";
if(my_ans != ans) {
break;
}
}
auto dur = duration_cast<milliseconds>(steady_clock::now()-stop).count();
cout << "Exec time: " << dur << " ms\n\n";
}
}
return 0;
}
/*
*/
