#include <bits/stdc++.h>
#define ll long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define F first
#define S second
using namespace std;
ll M, L, a[605], ans, b[605], dp[100005];
void upd(int count, int v, int w)
{
// cout << count << "s of " << v << " weighted " << w << '\n';
vector<int> cnt;
for(int j = 1; count >= j; j *= 2)
{
cnt.emplace_back(j);
count -= j;
}
cnt.emplace_back(count);
for(int j : cnt)
if(v > 0)
for(int k = M * M; k >= v * j; k--)
dp[k] = min(dp[k - v * j] + j * w, dp[k]);
else if(v < 0)
for(int k = 0; k <= M * M + v * j; k++)
dp[k] = min(dp[k - v * j] + j * w, dp[k]);
//for(int i = 0; i <= M * M; i++)
// cout << dp[i] << " \n"[i == M * M];
}
signed main()
{
// ios::sync_with_stdio(0);
// cin.tie(0), cout.tie(0);
cin >> M >> L;
for(int i = 1; i <= 2 * M + 1; i++)
cin >> a[i];
if(L < 0)
{
L = -L;
for(int i = 1; i <= M; i++)
swap(a[i], a[2 * M + 2 - i]);
}
for(int i = 1; i <= M; i++)
{
L += a[M + 1 - i] * i, ans += a[M + 1 - i];
swap(a[M + 1 - i], b[M + 1 - i]);
}
//cout << L << '\n';
ans += a[M + 1];
swap(a[M + 1], b[M + 1]);
for(int i = 1; i <= M; i++)
if(i * a[M + 1 + i] <= L)
{
ans += a[M + 1 + i];
L -= i * a[M + 1 + i];
b[M + 1 + i] = min(M, a[M + 1 + i]);
a[M + 1 + i] = 0;
}
else
{
ans += L / i;
b[i + M + 1] = min(M, L / i);
a[i + M + 1] = min(M, a[i + M + 1] - L / i);
L %= i;
}
for(int i = M; i >= 1; i--)
if(i * b[M + 1 - i] <= L)
{
ans -= b[M + 1 - i];
L -= i * b[M + 1 - i];
a[M + 1 - i] = min(M, b[M + 1 - i]);
b[M + 1 - i] = 0;
}
else
{
ans -= L / i;
a[M + 1 - i] = min(M, L / i);
b[M + 1 - i] = min(M, b[M + 1 - i] - L / i);
L %= i;
}
if(L > M)
{
cout << "impossible\n";
return 0;
}
//for(int i = 1; i <= M * 2 + 1; i++)
// cerr << a[i] << " \n"[i == 2 * M + 1];
//for(int i = 1; i <= M * 2 + 1; i++)
// cerr << b[i] << " \n"[i == 2 * M + 1];
//cerr << ans << " " << L << '\n';
for(int i = 0; i <= M * M; i++)
dp[i] = (i == 0 ? 0 : 1e18);
for(int i = 1; i <= M; i++)
upd(a[i + M + 1], i, -1);
for(int i = 1; i <= M; i++)
upd(b[M + 1 - i], i, 1);
for(int i = 1; i <= M; i++)
upd(b[M + i + 1], -i, 1);
for(int i = 1; i <= M; i++)
upd(a[M + 1 - i], -i, -1);
ans -= dp[L];
if(ans < 0)
cout << "impossible\n";
else cout << ans << '\n';
}
