#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];
long long dp[4*maxn*maxn];
long long tmp[4*maxn*maxn];
int main(){
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;
}
}
int sum = m*(m+1)*2;
memset(dp, -1, sizeof(dp));
dp[sum] = 0;
for(int b = 0; b <= 60; b++){
for(int i = 1; i <= m; i++){
memset(tmp, -1, sizeof(tmp));
for(int j = 0; j <= 2*sum; j++){
if(dp[j] == -1)continue;
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++){
int nw = j + (p_val - n_val)*i;
long long cost = p_val + n_val;
cost <<= b;
assert(0 <= nw && nw <= 2*sum);
tmp[nw] = max(tmp[nw], dp[j] + cost);
}
}
}
memcpy(dp, tmp, sizeof(dp));
}
for(int j = 0; j <= 2*sum; j++)tmp[j] = -1;
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[i]);
}
for(int i = 0; i <= 2*sum; i++)dp[i] = tmp[i];
}
if(dp[sum] == -1)cout << "impossible";
else cout << dp[sum] + A[m];
}
