#define DEBUG 0
#include <bits/stdc++.h>
using namespace std;
#if DEBUG
// basic debugging macros
int __i__,__j__;
#define printLine(l) for(__i__=0;__i__<l;__i__++){cout<<"-";}cout<<endl
#define printLine2(l,c) for(__i__=0;__i__<l;__i__++){cout<<c;}cout<<endl
#define printVar(n) cout<<#n<<": "<<n<<endl
#define printArr(a,l) cout<<#a<<": ";for(__i__=0;__i__<l;__i__++){cout<<a[__i__]<<" ";}cout<<endl
#define print2dArr(a,r,c) cout<<#a<<":\n";for(__i__=0;__i__<r;__i__++){for(__j__=0;__j__<c;__j__++){cout<<a[__i__][__j__]<<" ";}cout<<endl;}
#define print2dArr2(a,r,c,l) cout<<#a<<":\n";for(__i__=0;__i__<r;__i__++){for(__j__=0;__j__<c;__j__++){cout<<setw(l)<<setfill(' ')<<a[__i__][__j__]<<" ";}cout<<endl;}
// advanced debugging class
// debug 1,2,'A',"test";
class _Debug {
public:
template<typename T>
_Debug& operator,(T val) {
cout << val << endl;
return *this;
}
};
#define debug _Debug(),
#else
#define printLine(l)
#define printLine2(l,c)
#define printVar(n)
#define printArr(a,l)
#define print2dArr(a,r,c)
#define print2dArr2(a,r,c,l)
#define debug
#endif
// define
#define MAX_VAL 999999999
#define MAX_VAL_2 999999999999999999LL
#define EPS 1e-6
#define mp make_pair
#define pb push_back
// typedef
typedef unsigned int UI;
typedef long long int LLI;
typedef unsigned long long int ULLI;
typedef unsigned short int US;
typedef pair<int,int> pii;
typedef pair<LLI,LLI> plli;
typedef vector<int> vi;
typedef vector<LLI> vlli;
typedef vector<pii> vpii;
typedef vector<plli> vplli;
// ---------- END OF TEMPLATE ----------
LLI _A[601],*A = _A+300;
LLI _curr[601],*curr = _curr+300;
vpii poss;
int _dp[200001],*dp = _dp+100000;
int main() {
int i;
int M;
LLI L;
scanf("%d %lld",&M,&L);
for (i = -M; i <= M; i++) scanf("%lld",&A[i]);
LLI s1 = 0,s2 = 0,ans = 0;
for (i = 1; i <= M; i++) s1 += i*A[i];
for (i = -M; i <= -1; i++) s2 += i*A[i];
if ((L > s1) || (L < s2)) {
printf("impossible\n");
return 0;
}
LLI s = 0;
if (L >= s1+s2) {
for (i = 0; i <= M; i++) curr[i] = A[i],s += i*A[i];
for (i = -1; i >= -M; i--) curr[i] = min((s-L)/(-i),A[i]),s += i*curr[i];
}
else {
for (i = 0; i >= -M; i--) curr[i] = A[i],s += i*A[i];
for (i = 1; i <= M; i++) curr[i] = min((L-s)/i,A[i]),s += i*curr[i];
}
L -= s;
for (i = -M; i <= M; i++) {
ans += curr[i];
if (i != 0) {
int t = min(curr[i],(LLI) M);
if (t > 0) {
int k = 1;
while (t > k) t -= k,poss.pb(mp(-k*i,-k)),k *= 2;
poss.pb(mp(-t*i,-t));
}
t = min(A[i]-curr[i],(LLI) M);
if (t > 0) {
int k = 1;
while (t > k) t -= k,poss.pb(mp(k*i,k)),k *= 2;
poss.pb(mp(t*i,t));
}
}
}
random_shuffle(poss.begin(),poss.end());
int B = 100000;
fill(dp-B,dp+B+1,-1e9),dp[0] = 0;
for (auto [c,v]: poss) {
if (c > 0) {
for (i = B; i >= -B+c; i--) dp[i] = max(dp[i],dp[i-c]+v);
}
else {
for (i = -B; i <= B+c; i++) dp[i] = max(dp[i],dp[i-c]+v);
}
}
if (dp[L] < -1e8) printf("impossible\n");
else printf("%lld\n",ans+dp[L]);
return 0;
}
