#include <iostream>
#include <algorithm>
#include <cstdlib>

typedef long long ll;
typedef double lf;

// #define DEBUG 1
struct IO
{
    #define MAXSIZE (1 << 20)
    #define isdigit(x) (x >= '0' && x <= '9')
    char buf[MAXSIZE], *p1, *p2;
    char pbuf[MAXSIZE], *pp;
    #if DEBUG
    #else
    IO() : p1(buf), p2(buf), pp(pbuf) {}
    ~IO() {fwrite(pbuf, 1, pp - pbuf, stdout);}
    #endif
    #define gc() (p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, MAXSIZE, stdin), p1 == p2) ? ' ' : *p1++)
    #define blank(x) (x == ' ' || x == '\n' || x == '\r' || x == '\t')

    template <typename T>
    void Read(T &x)
    {
        #if DEBUG
        std::cin >> x;
        #else
        bool sign = 0; char ch = gc(); x = 0;
        for (; !isdigit(ch); ch = gc())
            if (ch == '-') sign = 1;
        for (; isdigit(ch); ch = gc()) x = x * 10 + (ch ^ 48);
        if (sign) x = -x;
        #endif
    }
    void Read(char *s)
    {
        #if DEBUG
        std::cin >> s;
        #else
        char ch = gc();
        for (; blank(ch); ch = gc());
        for (; !blank(ch); ch = gc()) *s++ = ch;
        *s = 0;
        #endif
    }
    void Read(char &c) {for (c = gc(); blank(c); c = gc());}

    void Push(const char &c)
    {
        #if DEBUG
        putchar(c);
        #else
        if (pp - pbuf == MAXSIZE) fwrite(pbuf, 1, MAXSIZE, stdout), pp = pbuf;
        *pp++ = c;
        #endif
    }
    template <typename T>
    void Write(T x)
    {
        if (x < 0) x = -x, Push('-');
        static T sta[35];
        int top = 0;
        do sta[top++] = x % 10, x /= 10; while (x);
        while (top) Push(sta[--top] ^ 48);
    }
    template <typename T>
    void Write(T x, char lst) {Write(x), Push(lst);}
} IO;
#define Read(x) IO.Read(x)
#define Write(x, y) IO.Write(x, y)
#define Put(x) IO.Push(x)

using namespace std;

const int MAXN = 310;

// #include <ctime>
// int st;

int n;
ll L, a[MAXN], b[MAXN], a0, all;
ll ap[MAXN], bp[MAXN], ans = 6e18;

const int MAXT = 8e8 + 5e7;
int T;


int DFS(int cur, ll s, ll cnt)
{
    // cout << cur << " " << s << " " << cnt << "\n";
    if (cur == 1)
    {
        T++;
        bool flag = 0;
        if (s + a[1] >= 0 && s - b[1] <= 0) ans = min(ans, cnt + (s > 0 ? s : -s)), flag = 1;
        if (T > MAXT)
        {
            if (ans == 6e18) cout << "impossible\n";
            else cout << all - ans + a0 << "\n";
            // cerr << 1.0 * (clock() - st) / CLOCKS_PER_SEC << "\n";
            exit(0);
        }
        return flag;
    }
    if (cnt >= ans) return 2;
    if (s + ap[cur] < 0 || s - bp[cur] > 0) return 2;
    int tp;
    if (s + cur * a[cur] <= 0)
    {
        for (ll i = a[cur]; i >= -b[cur]; i--)
        {
            tp = DFS(cur - 1, s + cur * i, cnt + (i > 0 ? i : -i));
            if (tp) return tp;
        }
        return 0;
    }
    else if (s - cur * b[cur] >= 0)
    {
        for (ll i = -b[cur]; i <= a[cur]; i++)
        {
            tp = DFS(cur - 1, s + cur * i, cnt + (i > 0 ? i : -i));
            if (tp) return tp;
        }
        return 0;
    }
    else
    {
        ll l, r;
        if (s < 0) l = (-s) / cur, r = l + 1;
        else l = -((s + cur - 1) / cur), r = l + 1;
        bool flag = 0;
        for (ll i = 0; i <= a[cur] + b[cur]; i++)
        {
            if (l < -b[cur] || (r <= a[cur] && s + r * cur < -(s + l * cur)))
                tp = DFS(cur - 1, s + r * cur, cnt + (r > 0 ? r : -r)), r++;
            else tp = DFS(cur - 1, s + l * cur, cnt + (l > 0 ? l : -l)), l--;
            if (tp == 1) flag = 1;
        }
        return flag;
    }
}

int main()
{
    // st = clock();
    // freopen("C.in", "r", stdin);
    #if DEBUG
    #else
    ios::sync_with_stdio(0), cin.tie(0);
    #endif
    Read(n), Read(L);
    for (int i = n; i >= 1; i--) Read(b[i]), all += b[i];
    Read(a0);
    ll sum = 0;
    for (int i = 1; i <= n; i++) Read(a[i]), sum += (a[i] - b[i]) * i, all += a[i];
    for (int i = 1; i <= n; i++) ap[i] = ap[i - 1] + a[i] * i, bp[i] = bp[i - 1] + b[i] * i;
    // cout << bp[n] << "\n";
    sum = L - sum;
    // cout << sum << "\n";
    DFS(n, sum, 0);
    if (ans == 6e18) cout << "impossible\n";
    else cout << all - ans + a0 << "\n";
    // cerr << 1.0 * (clock() - st) / CLOCKS_PER_SEC << " #\n";
    return 0;
}