/*#pragma GCC optimize("Ofast,unroll-loops")
#pragma comment(linker, "/stack:200000000")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,fma,tune=native")*/
/*#pragma GCC optimize("O2")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx,avx2,sse,sse2,fma")*/
#include <bits/stdc++.h>
using namespace std;
using ll=long long int;
using ld=long double;
using pll=pair<ll,ll>;
using pii=pair<int,int>;
using point=complex<double>;
#define F first
#define S second
//#define X real()
//#define Y imag()
#define pb push_back
#define mp make_pair
#define lc v<<1
#define rc v<<1|1
#define fast_io ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr)
#define kill(x) cout << x << '\n';exit(0)
#define killshayan kill("done!")
#define killmashtali kill("Hello, World!")
const int N=2e5+10,LN=20,M=1e6+10,SQ=700,BS=737,inf=1.05e9,NSQ=N/SQ+3;
const ll INF=1e18;
const double pi=acos(-1);
const ld ep=1e-7;
const int MH=1000696969,MD=998244353,MOD=1000000007;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define ordered_set tree<pii, null_type,greater<pii>, rb_tree_tag,tree_order_statistics_node_update>
ll pow(ll x, ll y, ll mod){
ll ans=1;
while (y != 0) {
if (y & 1) ans = ans * x % mod;
y >>= 1;
x = x * x % mod;
}
return ans;
}
ll n,l,*dp,ns,ps;
vector<pll> neg,pos;
int main(){
fast_io;
cin >> n >> l;
for(ll i=-n; i<0; i++){
ll x,t=1;
cin >> x;
ns+=x*i;
while(t<x){
neg.pb({i*t,t});
x-=t;
t*=2;
}
if(x) neg.pb({i*x,x});
}
for(ll i=0; i<=n; i++){
ll x,t=1;
cin >> x;
ps+=x*i;
while(t<x){
pos.pb({i*t,t});
x-=t;
t*=2;
}
if(x) pos.pb({i*x,x});
}
if(l<ns || l>ps){
cout << "impossible\n";
return 0;
}
dp=new ll[abs(ns)+ps+1]+abs(ns);
for(ll i=ns; i<=ps; i++) dp[i]=-INF;
dp[0]=0;
for(auto [x,y] : neg){
for(ll i=ns; i<=ps; i++){
if(i-x<=ps) dp[i]=max(dp[i],dp[i-x]+y);
}
}
for(auto [x,y] : pos){
for(ll i=ps; i>=ns; i--){
if(i-x>=ns) dp[i]=max(dp[i],dp[i-x]+y);
}
}
if(dp[l]<0) cout << "impossible\n";
else cout << dp[l] << '\n';
return 0;
}
