#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

const int MX=605, SUM=2e5+5;

ll M,L;
ll _A[MX], _B[MX];
auto A=_A+300, B=_B+300;

ll _dp[SUM], _ndp[SUM];
auto dp=_dp+100000, ndp=_ndp+100000;

int main() {
        cin.tie(0); ios_base::sync_with_stdio(0);

        cin>>M>>L;

        for(int i=-M;i<=M;i++) cin>>A[i];

        ll sum=0;
        
        if(L<0) {
                for(int i=1;i<=M;i++) swap(A[-i],A[i]);
                L=-L;
        }
        
        for(int i=-M;i<=M;i++) {
                sum+=i*A[i];
        }

        ll cur=0, taken=0;
        if(sum>=L) {
                for(int i=-M;i<=0;i++) {
                        B[i]=A[i];
                        cur+=i*B[i];
                        taken+=B[i];
                }
                for(int i=1;i<=M;i++) {
                        B[i]=min(A[i],(L-cur)/i);
                        cur+=i*B[i];
                        taken+=B[i];
                }
        } else {
                for(int i=0;i<=M;i++) {
                        B[i]=A[i];
                        cur+=i*B[i];
                        taken+=B[i];
                }

                if(cur<L) {
                        cout<<"impossible"<<'\n';
                        return 0;
                }

                for(int i=-1;i>=-M;i--) {
                        int j=-i;
                        B[i]=min(A[i],(cur-L)/j);
                        cur+=i*B[i];
                        taken+=B[i];
                }
        }

        for(int s=-100000;s<=100000;s++) {
                dp[s]=-1e18;
                ndp[s]=-1e18;
        }

        dp[0]=0;
        for(int i=-M;i<=M;i++) {
                vector<ll> v;

                ll x=A[i]-B[i];
                for(int k=0;k<40;k++) {
                        if(x>=(1LL<<k)) {
                                x-=(1LL<<k);
                                v.push_back(1LL<<k);
                        }
                }
                v.push_back(x);

                // add Ai - Bi
                for(auto k:v) {
                        for(int s=-100000;s<=100000;s++) {
                                ndp[s]=max(ndp[s],dp[s]);
                                if(s+i*k<=-100000 || s+i*k>=100000 || dp[s]==-1e18) continue;
                                ndp[s+i*k]=max(ndp[s+i*k],dp[s]+k);
                        }
                        for(int s=-100000;s<=100000;s++) {
                                dp[s]=ndp[s];
                                ndp[s]=-1e18;
                        }
                }

                v.clear();      
                x=B[i];
                for(int k=0;k<40;k++) {
                        if(x>=(1LL<<k)) {
                                x-=(1LL<<k);
                                v.push_back(1LL<<k);
                        }
                }
                v.push_back(x);

                // remove Bi
                for(auto k:v) {
                        for(int s=-100000;s<=100000;s++) {
                                ndp[s]=max(ndp[s],dp[s]);
                                if(s-i*k<=-100000 || s-i*k>=100000 || dp[s]==-1e18) continue;
                                ndp[s-i*k]=max(ndp[s-i*k],dp[s]-k);     
                        }
                        for(int s=-100000;s<=100000;s++) {
                                dp[s]=ndp[s];
                                ndp[s]=-1e18;
                        }
                }
        }

        if(L-cur<=-100000 || L-cur>=100000 || dp[L-cur]==-1e18) {
                cout<<"impossible"<<'\n';
                return 0;
        }

        cout<<dp[L-cur]+taken<<'\n';
}