#include <stdio.h>
#include <string.h>
#define N 100
#define INF 0x3f3f3f3f
long long min(long long a, long long b) { return a < b ? a : b; }
long long max(long long a, long long b) { return a > b ? a : b; }
void update(int *dp, int s_, int a, int k, int c) {
static int dq[N * N * 2 + 1], qu[N * N * 2 + 1];
int s, r, head, cnt;
if (a > 0) {
for (s = 0; s <= s_; s++)
dq[s] = dp[s] == -INF ? -INF : dp[s] - s / a * c;
for (r = 0; r < a; r++) {
head = cnt = 0;
for (s = r; s <= s_; s += a) {
if (dq[s] != -INF) {
while (cnt && dq[qu[head + cnt - 1]] < dq[s])
cnt--;
qu[head + cnt++] = s;
}
dp[s] = cnt == 0 ? -INF : dq[qu[head]] + s / a * c;
if (cnt && qu[head] == s - a * k)
head++, cnt--;
}
}
} else if (a < 0) {
a = -a;
for (s = 0; s <= s_; s++)
dq[s] = dp[s] == -INF ? -INF : dp[s] + s / a * c;
for (r = 0; r < a; r++) {
head = cnt = 0;
for (s = (s_ - r) / a * a + r; s >= 0; s -= a) {
if (dq[s] != -INF) {
while (cnt && dq[qu[head + cnt - 1]] < dq[s])
cnt--;
qu[head + cnt++] = s;
}
dp[s] = cnt == 0 ? -INF : dq[qu[head]] - s / a * c;
if (cnt && qu[head] == s + a * k)
head++, cnt--;
}
}
} else {
if (c <= 0)
return;
for (s = 0; s <= s_; s++)
if (dp[s] != -INF)
dp[s] += k * c;
}
}
long long solve(long long *kk, int n, long long s_) {
static int dp[N * N * 2 + 1], dq[N + 1][N * N + 1];
int a;
long long s, s0, s1, s2, k, k0, ans;
for (s = 0; s <= n * n; s++)
dp[s] = -INF;
dp[0] = 0;
for (a = n; a >= 0; a--) {
memcpy(dq[a], dp, (n * n + 1) * sizeof *dp);
update(dp, n * n, a, min(kk[n + a], n), 1);
}
for (s = 0; s <= n * n * 2; s++)
dp[s] = -INF;
dp[n * n + 0] = 0;
s0 = 0, k0 = 0;
for (a = -n; a < 0; a++) {
update(dp, n * n * 2, a, min(kk[n + a], n), -1);
s0 += kk[n + a] * a, k0 += kk[n + a];
}
ans = -INF;
for (a = 0; a <= n; a++) {
for (s1 = 0; s1 <= n * n * 2; s1++)
if (dp[s1] != -INF) {
s2 = s_ + s1 - s0 - n * n;
if (a == 0) {
if (s2 >= 0 && s2 <= n * n && dq[a][s2] != -INF)
ans = max(ans, k0 + dp[s1] + dq[a][s2] + kk[n + a]);
} else
for (s2 = (s2 % a + a) % a; s2 <= n * n; s2 += a)
if (dq[a][s2] != -INF) {
s = s0 - (s1 - n * n) + s2;
if (s <= s_ && (s_ - s) % a == 0 && (k = (s_ - s) / a) <= kk[n + a])
ans = max(ans, k0 + dp[s1] + dq[a][s2] + k);
}
}
update(dp, n * n * 2, a, min(kk[n + a], n), -1);
s0 += kk[n + a] * a, k0 += kk[n + a];
}
return ans;
}
int main() {
static long long kk[N * 2 + 1];
int n, a, r;
long long s, ans, tmp;
scanf("%d%lld", &n, &s);
for (a = -n; a <= n; a++)
scanf("%lld", &kk[n + a]);
ans = -INF;
for (r = 0; r < 2; r++) {
ans = max(ans, solve(kk, n, s));
for (a = 1; a <= n; a++)
tmp = kk[n - a], kk[n - a] = kk[n + a], kk[n + a] = tmp;
s = -s;
}
if (ans == -INF)
printf("impossible\n");
else
printf("%lld\n", ans);
return 0;
}
