#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(int a)
{
vi ans;
int i = 0;
while ((1 << i) <= a)
{
a -= (1 << i);
ans.push_back(i++);
}
while (i > 0)
if ((1 << --i) <= a)
ans.push_back(i), a -= (1 << i);
return ans;
}
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];
int an = accumulate(A.begin(), A.begin() + M, 0);
int ap = accumulate(A.begin() + M + 1, A.begin() + 2 * M + 1, 0);
int MAXSIZE = 2 * M * max(an, ap) + 2;
vi dp(MAXSIZE, -1);
ll center = MAXSIZE / 2;
dp[center] = A[M];
for (int foo = 0; foo < 2; ++foo)
{
reverse(all(A)), reverse(all(dp));
for (ll m = 1; m <= M; ++m)
{
ll maxNum = A[m + M];
vi shifts = calcShifts(maxNum);
for (int i : shifts)
{
ll amount = (1 << i);
ll d = amount * m;
for (int j = sz(dp) - 1; j >= d; --j)
dp[j] = max(dp[j], (dp[j - d] != -1) ? dp[j - d] + amount : -1);
}
}
}
ll ans = -1;
if (0 <= center + L && center + L < sz(dp))
ans = dp[center + L];
if (ans == -1)
cout << "impossible\n";
else
cout << ans << "\n";
return 0;
}
