#include<bits/stdc++.h>
using namespace std;
namespace my_std{
	#define ll long long
	#define bl bool
	ll my_pow(ll a,ll b,ll mod){
		ll res=1;
		if(!b) return 1;
		while(b){
			if(b&1) res=(res*a)%mod;
			a=(a*a)%mod;
			b>>=1;
		}
		return res;
	}
	ll qpow(ll a,ll b){
		ll res=1;
		if(!b) return 1;
		while(b){
			if(b&1) res*=a;
			a*=a;
			b>>=1;
		}
		return res;
	}
	#define db double
	#define pf printf
	#define pc putchar
	#define fr(i,x,y) for(register ll i=(x);i<=(y);i++)
	#define pfr(i,x,y) for(register ll i=(x);i>=(y);i--)
	#define go(u) for(ll i=head[u];i;i=e[i].nxt)
	#define enter pc('\n')
	#define space pc(' ')
	#define fir first
	#define sec second
	#define MP make_pair
	#define il inline
	#define inf 1e16
	#define random(x) rand()*rand()%(x)
	#define inv(a,mod) my_pow((a),(mod-2),(mod))
	il ll read(){
		ll sum=0,f=1;
		char ch=0;
		while(!isdigit(ch)){
			if(ch=='-') f=-1;
			ch=getchar();
		}
		while(isdigit(ch)){
			sum=sum*10+(ch^48);
			ch=getchar();
		}
		return sum*f;
	}
	il void write(ll x){
		if(x<0){
			x=-x;
			pc('-');
		}
		if(x>9) write(x/10);
		pc(x%10+'0');
	}
	il void writeln(ll x){
		write(x);
		enter;
	}
	il void writesp(ll x){
		write(x);
		space;
	}
}
using namespace my_std;
ll n,m,a[660],b[660],sum=0,f[400040],g[400040],ans=0;
ll q[400040],l,r;
void ins(ll v,ll x,ll cnt){
	if(!v) return;
	fr(i,0,4*n*n) g[i]=f[i];
	if(v>0){
		fr(i,0,v-1){
			l=1;
			r=0;
			for(ll j=i,k=0;j<=4*n*n;j+=v,k++){
				while(l<=r&&q[l]<(k-cnt)) l++;
				if(l<=r) f[j]=max(f[j],g[q[l]*v+i]+x*(k-q[l]));
				while(l<=r&&(g[q[r]*v+i]-x*q[r])<=(g[j]-x*k)) r--;
				q[++r]=k;
			}
		}
	}
	else{
		v=-v;
		fr(i,0,v-1){
			l=1;
			r=0;
			ll ed=i;
			while(ed<=4*n*n) ed+=v;
			ed-=v;
			for(ll j=ed,k=0;j>=0;j-=v,k++){
				while(l<=r&&q[l]<(k-cnt)) l++;
				if(l<=r) f[j]=max(f[j],g[ed-q[l]*v]+x*(k-q[l]));
				while(l<=r&&(g[ed-q[r]*v]-x*q[r])<=(g[j]-x*k)) r--;
				q[++r]=k;
			}
		}
	}
}
int main(){
	n=read();
	m=read();
	fr(i,-n,n){
		a[n+i]=read();
		sum+=i*a[n+i];
	}
	if(sum<m){
		m=-m;
		reverse(a,a+2*n+1);
	}
	sum=0;
	fr(i,-n,0){
		sum+=i*a[n+i];
		ans+=a[n+i];
	}
	if(sum>m){
		pf("impossible");
		return 0;
	}
	fr(i,1,n){
		if((sum+i*a[n+i])<=m){
			b[n+i]=a[n+i];
			sum+=i*a[n+i];
			ans+=a[n+i];
		}
		else{
			b[n+i]=(m-sum)/i;
			sum+=i*b[n+i];
			ans+=b[n+i];
			break;
		}
	}
	fr(i,0,4*n*n) f[i]=-inf;
	f[2*n*n-m+sum]=0;
	fr(i,-n,0) ins(-i,-1,min(2*n,a[n+i]));
	fr(i,1,n){
		ins(-i,-1,min(2*n,b[n+i]));
		ins(i,1,min(2*n,a[n+i]-b[n+i]));
	}
	if((ans+f[2*n*n])<0) pf("impossible");
	else write(ans+f[2*n*n]);
}