#include <bits/stdc++.h>

using namespace std;

const int N = 305;

long long _a[N << 1], *a = _a + N, _b[N << 1], *b = _b + N, _f[N * N * 2], *f = _f + N * N;

void append(long long v, long long w, long long L) {
    if (v > 0) {
        for (long long i = L; i >= -L + v; --i) f[i] = max(f[i], f[i - v] + w);
    } else {
        for (long long i = -L; i <= L + v; ++i) f[i] = max(f[i], f[i - v] + w);
    }
}

void apd(long long v, long long w, long long k, long long L) {
    if (!v) return;
    for (long long i = 1; i <= k; i <<= 1) {
        if (k >= i) append(v * i, w * i, L), k -= i;
    }
    append(v * k, w * k, L);
}

signed main() {
    int n; scanf("%d", &n);
    long long L; scanf("%lld", &L);
    for (int i = -n; i <= n; ++i) scanf("%lld", &a[i]), L -= a[i] * i, b[i] = a[i];
    if (L < 0) reverse(a - n, a + n + 1), reverse(b - n, b + n + 1), L = -L;
    for (int i = -n; i; ++i) {
        long long t = min(L / -i, a[i]);
        L += i * t, b[i] -= t;
    }
    if (L > n * n) return 0 & puts("impossible");
    memset(_f, -0x3f, sizeof(_f));
    f[0] = 0;
    for (int i = -n; i <= n; ++i) {
        apd(-i, -1, b[i], n * n), apd(i, 1, a[i] - b[i], n * n);
    }
    if (f[L] < -1e9) return 0 & puts("impossible");
    else printf("%lld\n", accumulate(b - n, b + n + 1, 0ll) + f[L]);
    return 0;
}