#include<bits/stdc++.h>
using namespace std;

const long long INF = 1e18;
const int maxn = 305;

long long A[2*maxn], inp[2*maxn];

int bs_A[2*maxn][65];

vector<pair<int, long long>> g[65][maxn];

long long dp[2][4*maxn*maxn];
long long tmp[4*maxn*maxn];

long long mx(const long long &a, const long long &b){return a > b ? a : b;}

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	int m;
	long long L;
	cin >> m >> L;
	for(int i = 0; i <= 2*m; i++)cin >> A[i];
	if(L < 0){
		L*=-1;
		for(int i = 1; i <= m; i++)swap(A[m-i], A[m+i]);
	}
	for(int i = 0; i <= 2*m; i++){
		if(i == m)continue;
		for(int j = 0; j <= 60; j++){
			if(A[i] == 0)break;
			bs_A[i][j] = A[i]&1 ? 1 : 2;
			A[i] = (A[i]-1)/2;
		}
	}
	for(int b = 0; b <= 60; b++){
		for(int i = 1; i <= m; i++){
			map<int, long long> mp;
			for(int p_val = 0; p_val <= bs_A[m+i][b]; p_val++){
				for(int n_val = 0; n_val <= bs_A[m-i][b]; n_val++){
					mp[(p_val - n_val)*i] = max<long long>(mp[(p_val - n_val)*i], p_val + n_val);
				}
			}	
			for(auto v: mp)g[b][i].push_back({v.first, v.second<<b});
		}
	}
	int sum = m*(m+1)*2;
	for(int i = 0; i <= 2*sum; i++)dp[0][i] = dp[1][i] = -INF;
	dp[0][sum] = 0;
	for(int b = 0; b <= 50; b++){
		for(int i = 0; i <= 2*m; i++){
			for(int j = 0; j <= 2*sum; j++)dp[i&1][j] = max(dp[i&1][j], dp[(i&1)^1][j]);
			for(int l = 1; l <= bs_A[i][b]; l++){
				int val = (m-i)*l;
				
			}
			for(auto v: g[b][i])for(int j = (v.first > 0 ? 0 : -v.first); j <= (v.first > 0 ? 2*sum - v.first : 2*sum); j++)dp[i&1][j + v.first] = mx(dp[i&1][j + v.first], dp[(i&1)^1][j] + v.second);
		}
		for(int j = 0; j <= 2*sum; j++)tmp[j] = -INF; 
		for(int i = 0; i <= 2*sum; i++){
			if(((i&1)^(sum&1)) != ((L>>b)&1))continue;
			int ri = i - sum, pos;
			if(ri < 0)pos = (ri-1)/2 + sum;
			else pos = ri/2 + sum;
			assert(pos >= 0 && pos <= 2*sum);
			tmp[pos] = max(tmp[pos], dp[0][i]);
		}
		for(int i = 0; i <= 2*sum; i++){
			dp[0][i] = tmp[i];
			dp[1][i] = -INF;
		}
	}
	if(dp[0][sum] < 0)cout << "impossible";
	else cout << dp[0][sum] + A[m];
}