#include <bits/stdc++.h>
using namespace std;
#define all(a) a.begin(),a.end()
#define owo ios_base::sync_with_stdio(0);cin.tie(0);
typedef long long int ll;
ll a[5000];
ll take[5000];
struct item{
ll w = 0,v = 0,c = 0;
item(){}
item(ll a,ll b,ll _c){
w = a;
v = b;
c = _c;
}
};
int main()
{
ll m,L;
cin>>m>>L;
for(int i=-m;i<=m;i++)cin>>a[i+m];
//greedy sol and optimal sol distance small
ll neg = 0,pos = 0;
for(ll i=-m;i<=0;i++)neg+=i*a[i+m];
for(ll i=0;i<=m;i++)pos+=i*a[i+m];
if(L>pos || L < neg){
cout<<"impossible";
return 0;
}
if(neg+pos < L){
for(int i=1;i<=m;i++)swap(a[i+m],a[-i+m]);
L*=-1;
}
ll sum = 0;
ll cur = a[m];
vector<item>b;
for(ll i=-m;i<=-1;i++){
sum+=a[i+m] * i;
cur+=a[i+m];
a[i+m] = min(a[i+m],2*m);
if(a[i+m])b.push_back(item(i,-1,a[i+m]));
}
//weight value count
for(int i=1;i<=m;i++){
take[i] = min(a[i+m],(L-sum)/i);
a[i+m]-=take[i];
cur+=take[i];
sum+=i*1LL*take[i]; //add smtg
if(a[i+m])b.push_back(item(i,1,min(2*m,a[i+m])));
}
for(int i=1;i<=m;i++){ //take smtg away
if(take[i])b.push_back(item(-i,-1,min(2*m,take[i])));
}
int mx = 2*m*m;
const ll INF = 1e18;
vector<ll>dp(mx+1,-INF);
dp[0] = 0;
for(auto x:b){
int z = 1;
vector<int>cc;
while(x.c>=z){
cc.push_back(z);
x.c-=z;
z*=2;
}
if(x.c)cc.push_back(x.c);
if(x.w > 0){
for(int y : cc){
for(int i=mx;i >= y * x.w;i--){
if(dp[i-y * x.w] != -INF)dp[i] = max(dp[i],dp[i - y * x.w] + y * x.v);
}
}
}else{
for(int y : cc){
for(int i=0;i <= mx + y * x.w;i++){
if(dp[i - y * x.w] != -INF)dp[i] = max(dp[i],dp[i - y * x.w] + y * x.v);
}
}
}
}
if(dp[L-sum] != -INF)cout<<cur+dp[L-sum];
else cout<<"impossible";
}
