#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll MAX = 50*100*101;
const ll INF = 1e18;
ll solve(ll M, ll L, vector<ll> a){
vector<ll> dp(2*MAX+1, -INF);
dp[MAX] = 0;
for(int i = 0; i < 2*M+1; ++i){
if(i == M){
for(int j = 0; j < 2*MAX+1; ++j) dp[j] += a[M];
continue;
}
int v = (int)(i-M);
int start = 0;
if(v < 0) start = (int)(2*MAX+1+v);
for(int j = start; j < start + abs(v); ++j){
deque<pair<ll, int>> q;
for(int k = 0; j+v*k >= 0 && j+v*k < 2*MAX+1; ++k){
ll x = dp[j+v*k]-k;
while(!q.empty() && x > q.back().first) q.pop_back();
q.emplace_back(x, k);
if(k - q.front().second > min(a[i], M)) q.pop_front();
dp[j+v*k] = q.front().first + k;
}
}
}
ll ans = -INF;
if(L <= MAX && L >= -MAX) ans = dp[MAX+L];
ll sum = 0;
ll taken = 0;
for(int i = 0; i < M; ++i){
if(a[i] > M){
sum += (a[i]-M)*(i-M);
taken += a[i]-M;
}
}
for(int i = 1; i <= M; ++i){
if(L-sum >= -MAX && L-sum <= MAX) ans = max(ans, taken+dp[MAX+L-sum]);
if(a[M+i] <= M) continue;
ll take = max(0ll, min(a[M+i]-M, (L-MAX-sum) / i));
for(; sum+take*i <= L+MAX && take <= a[M+i]-M; take++){
ll nsum = sum+take*i;
if(L-nsum >= -MAX && L-nsum <= MAX) ans = max(ans, taken+take+dp[MAX+L-nsum]);
}
take--;
sum += take*i;
taken += take;
}
return ans;
}
int main(){
cin.tie(0);
ios_base::sync_with_stdio(false);
ll M, L;
cin >> M >> L;
vector<ll> a(2*M+1);
for(int i = 0; i < 2*M+1; ++i) cin >> a[i];
ll ans = solve(M, L, a);
reverse(a.begin(), a.end());
ans = max(ans, solve(M, -L, a));
if(ans < 0) cout << "impossible\n";
else cout << ans << "\n";
}
