#include <bits/stdc++.h>
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("Ofast")
#define int long long
using namespace std;
const int M = 300 + 11;
const int X = M * M;
const int INF = 1LL << 60;
int a[M * 2];
int s[M * 2];
int norm(int x, int m){
if(x >= 0) return x;
return (x % m + m) % m;
}
int dp_p[M][X], dp_n[M][X];
void solve(int m, int L, vector<int> a, int dp[M][X]){
for(int i = 0; i <= m; i++){
fill(dp[i], dp[i] + X, -INF);
}
for(int i = 1; i <= m; i++) s[i] = min(L, s[i - 1] + i * a[i]);
dp[0][0] = 0;
for(int i = 1; i <= m; i++){
for(int j = 0; j <= m * (i - 1); j++){
int left = norm(s[i] - s[i - 1] + j - a[i] * i, i);
int right = min(s[i] + j - s[i - 1], m * i);
int inc = i;
int delta = ((s[i] - left) - (s[i - 1] - j)) / i;
for(int k = left; k <= right; k += inc){
dp[i][k] = max(dp[i][k], dp[i - 1][j] + delta);
delta--;
}
}
}
}
int32_t main(){
int m, L; cin >> m >> L;
for(int i = 0; i <= m * 2; i++) cin >> a[i];
if(L < 0){
reverse(a, a + m * 2 + 1); L = -L;
}
int sum_p = 0, sum_n = 0;
for(int i = m + 1; i <= m * 2; i++) {
sum_p += (i - m) * a[i];
}
for(int i = m - 1; i >= 0; i--) {
sum_n += (m - i) * a[i];
}
if(sum_p < L){
cout << "impossible" << endl;
return 0;
}
int lim = min(sum_n, sum_p - L);
// positive
vector<int> b_pos {0}, b_neg {0};
for(int i = 1; i <= m; i++){
b_pos.push_back(a[m + i]);
b_neg.push_back(a[m - i]);
}
solve(m, lim + L, b_pos, dp_p);
solve(m, lim, b_neg, dp_n);
int ans = -INF;
for(int i = 0; i <= m * m; i++){
ans = max(ans, dp_p[m][i] + dp_n[m][i]);
}
if(ans <= -INF / 2){
cout << "impossible" << endl;
}else{
cout << a[m] + ans << endl;
}
}
