#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pii;
typedef vector<pii> vpii;
typedef vector<ll> vi;
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
vi calcShifts(ll a)
{
vi ans;
ll i = 0;
while ((1LL << i) <= a)
{
a -= (1LL << i);
ans.push_back(i++);
}
while (i > 0)
if ((1LL << --i) <= a)
ans.push_back(i), a -= (1 << i);
return ans;
}
vi dp;
ll center;
void initDP(ll M, ll zero)
{
center = M * M;
dp.assign(2 * center + 1, INT_MIN);
assert(0 <= center + zero && center + zero < sz(dp));
dp[center + zero] = 0;
}
void addToDP(ll lift, ll maxNum)
{
ll f = (maxNum < 0) ? -1 : 1;
vi shifts = calcShifts(abs(maxNum));
for (int i : shifts)
{
ll amount = f * (1 << i);
ll d = amount * lift;
if (d > 0)
{
for (int j = sz(dp) - 1; j >= d; --j)
dp[j] = max(dp[j], (dp[j - d] != INT_MIN) ? dp[j - d] + amount : INT_MIN);
}
else
{
for (int j = 0; j < sz(dp) - abs(d); ++j)
dp[j] = max(dp[j], (dp[j - d] != INT_MIN) ? dp[j - d] + amount : INT_MIN);
}
}
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);
ll M, L;
cin >> M >> L;
vi A(2 * M + 1);
for (int i = 0; i < sz(A); ++i)
cin >> A[i];
ll totalSum = 0;
for (int i = 0; i < sz(A); ++i)
totalSum += (i - M) * A[i];
if (totalSum < L)
{
reverse(all(A));
totalSum *= -1;
L *= -1;
}
// find last Prefix position { i, idx } with pref <= L, or { sz(A)-1 = 2 * M, A[2 * M] }
int i = 0;
ll tmpans = 0, pref = 0;
vpii toadd;
for (; i < M; ++i)
{ // taking all negative values
tmpans += A[i];
pref += A[i] * (i - M);
toadd.push_back({i - M, max(-A[i], -M)});
}
while (i < sz(A) && pref + A[i] * (i - M) < L)
{
pref += A[i] * (i - M);
tmpans += A[i];
toadd.push_back({i - M, max(-A[i], -M)});
++i;
}
if (i == sz(A) || L - pref < 0)
{
cout << "impossible\n";
return 0;
}
assert(L - pref >= 0); // The expectation after the while loop is, that one is able to forfill this shit with the A[i] * (i - M) stuff
ll l = (L - pref) / (i - M);
pref += l * (i - M);
tmpans += l;
toadd.push_back({i - M, max(-l, -M)});
toadd.push_back({i - M, min(A[i] - l, M)});
for (int j = i + 1; j < sz(A); ++j)
toadd.push_back({j - M, min(A[j], M)});
initDP(M, pref - L);
for (pii add : toadd)
addToDP(add.first, add.second);
ll ans = INT_MIN;
if (dp[center] != INT_MIN)
ans = tmpans + dp[center];
if (ans == INT_MIN)
cout
<< "impossible\n";
else
cout << ans << "\n";
return 0;
}
