#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
const int MAX_M = 300;
int MAX_S;
int MIN_S;
const long long INF = 1e18;
int m;
unordered_map<int, long long> tk, ntk;
unordered_map<int, long long> dp, dpp;
void add(int x, int i)
{
swap(dp, dpp);
for(int s = MIN_S; s <= MAX_S; s ++)
dp[s] = dpp[s];
for(int s = MIN_S; s - i * x <= MAX_S; s ++)
if(MIN_S <= s - i * x && s - i * x <= MAX_S)
dp[s] = max(dp[s], dpp[s - i * x] + x);
for(int s = MIN_S; s <= MAX_S; s ++)
dp[s] = (dp[s] <= -INF + m ? -INF : dp[s]);
}
void substract(int x, int i)
{
swap(dp, dpp);
for(int s = MIN_S; s <= MAX_S; s ++)
dp[s] = dpp[s];
for(int s = MIN_S; s <= MAX_S; s ++)
if(MIN_S <= s + i * x && s + i * x <= MAX_S)
dp[s] = max(dp[s], dpp[s + i * x] - x);
for(int s = MIN_S; s <= MAX_S; s ++)
dp[s] = (dp[s] <= -INF + m ? -INF : dp[s]);
}
void afis()
{
for(int s = MIN_S; s <= MAX_S; s ++)
cout << dp[s] << " ";
cout << "\n";
}
int main()
{
long long l, u = 0, t = 0;
cin >> m >> l;
MIN_S = -m * m;
MAX_S = m * m;
for(int i = -m; i <= m; i ++)
{
cin >> ntk[i];
u += ntk[i];
}
if(l < 0)
{
for(int i = 1; i <= m; i ++)
swap(ntk[i], ntk[-i]);
l = -l;
}
long long s = 0;
for(int i = -m; i <= 0; i ++)
{
long long x = ntk[i];
s += i * x;
tk[i] += x;
ntk[i] -= x;
t += x;
u -= x;
}
for(int i = 1; i <= m; i ++)
{
long long x = min(ntk[i], (l - s) / i);
s += i * x;
tk[i] += x;
ntk[i] -= x;
t += x;
u -= x;
}
if(s + m < l)
{
for(int i = -m; i < 0; i ++)
{
long long x = min(tk[i], (l - s) / (-i));
s -= i * x;
tk[i] -= x;
ntk[i] += x;
t -= x;
u += x;
}
}
for(int s = MIN_S; s <= MAX_S; s ++)
dp[s] = -INF;
dp[0] = 0;
for(int i = -m; i <= m; i ++)
{
int k, s;
s = 0;
k = min((long long)m, ntk[i]);
for(int b = 0; s + (1 << b) <= k; s += (1 << b), b ++)
add((1 << b), i);
add(k - s, i);
s = 0;
k = min((long long)m, tk[i]);
for(int b = 0; s + (1 << b) <= k; s += (1 << b), b ++)
substract((1 << b), i);
substract(k - s, i);
}
if(l - s > MAX_S || dp[l - s] == -INF)
cout << "impossible\n";
else
cout << t + dp[l - s] << '\n';
return 0;
}
