#include<bits/stdc++.h>
#define pb push_back
#define pf push_front
#define mp make_pair
#define F first
#define S second
#define ff first
#define ss second
#define str string
#define ll long long
#define ull unsigned ll
#define ld long double
#define pll pair<ll,ll>
#define plll pair<pll,ll>
#define pllll pair<pll,pll>
#define pii pair<int,int>
#define pld pair<ld,ld>
#define vl vector<ll>
#define vll vector<pll>
#define vlll vector<plll>
#define vllll vector<pllll>
#define vb vector<bool>
#define vi vector<int>
#define vii vector<pii>
#define sz(x) (ll)(x).size()
#define fr front()
#define tp top()
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define bk back();
#pragma GCC target( "sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize("Ofast,unroll-loops,fast-math,O3")
using namespace std;
const ld pi=acos(-1.0);
const ll e5=1e5;
const ll e6=1e6;
const ll e9=1e9;
const ll inf=1e18;
const ll mod=1e9+7;
const ll mod2=998244353;
const ll MOD=106710087877475399;
const ll N=1e3+10;
const ll M=3e5+10;
const ld eps=1e-9;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll bpm(ll x,ll y,ll m){if(y==0)return 1%m;ll p=bpm(x,y/2,m);
if(y%2==0)return p*p%m;else return p*p%m*x%m;}
ll bp(ll x,ll y){if(y==0)return 1;ll p=bp(x,y/2);
if(y%2==0)return p*p;else return p*p*x;}
ll n,L,a[N],dp[M][2];
void solve(){
cin>>n>>L;
vl v;
for(ll i=-n;i<=n;i++){
ll x; cin>>x;
for(ll j=1;j<=x;j++) v.pb(i);
}
for(ll i=0;i<=3e5;i++) dp[i][1]=-inf;
dp[150000][1]=0;
for(ll i=0;i<sz(v);i++){
ll i2=i%2;
for(ll j=0;j<=3e5;j++){
dp[j][i2]=dp[j][i2^1];
if(0<=j-v[i]&&j-v[i]<=3e5) dp[j][i2]=max(dp[j][i2],dp[j-v[i]][i2^1]+1);
}
}
if(L>150000||L<-150000||dp[L+150000][1-sz(v)%2]<0) cout<<"impossible";
else cout<<dp[L+150000][1-sz(v)%2];
return;
}
int main(/*Aldk*/){
ios_base::sync_with_stdio(false); cin.tie(NULL);
//freopen("01.in", "r", stdin);
//freopen("01.out ", "w", stdout);
//cout<<setprecision(6)<<fixed;
int test=1;
//cin>>test;
for(int i=1;i<=test;i++){
solve();
cout<<'\n';
}
return 0;
}
