#include <cstdio>
#include <vector>
#include <iostream>
using namespace std;
const int M = 605,NV=300;
#define int long long
const int inf = 1e18;
#define pb push_back
int read()
{
	int x=0,f=1;char c;
	while((c=getchar())<'0' || c>'9') {if(c=='-') f=-1;}
	while(c>='0' && c<='9') {x=(x<<3)+(x<<1)+(c^48);c=getchar();}
	return x*f;
}
int n,m,a[M],dp[2][2*NV*NV+5];vector<int> v[M];
signed main()
{
    n=read();m=read();
    for(int i=0;i<=(n<<1);i++)
    {
        a[i]=read();
        if(i==n) continue;
        for(int j=0;j<=40;j++) if((1ll<<j)<=a[i])
            v[j].pb(i-n),a[i]-=(1ll<<j);
        for(int j=40;j>=0;j--) if((1ll<<j)<=a[i])
            v[j].pb(i-n),a[i]-=(1ll<<j);
    }
    int e=0,t=1,L=NV*NV,R=NV*NV;dp[0][NV*NV]=inf;
    //都增加inf，这样0就相当于-inf
    for(int i=0;i<=40;i++)
    {
        for(int d:v[i])
        {
            e^=1;t^=1;
            int tl=min(L,max(0ll,L+d));
            int tr=max(R,min(2*NV*NV,R+d));
            for(int j=L;j<=R;j++) dp[e][j]=dp[t][j];
            for(int j=tl;j<L;j++) dp[e][j]=0;
            for(int j=R+1;j<=tr;j++) dp[e][j]=0;
            for(int j=L,k;j<=R;j++) if((k=j+d)>=0 && k<=2*NV*NV)
                dp[e][k]=max(dp[e][k],dp[t][j]+(1ll<<i));
            L=tl;R=tr;
        }
        e^=1;t^=1;
        for(int j=L;j<=R;j++) dp[e][j]=0;
        int tl=NV*NV,tr=NV*NV;
        for(int j=L,k;j<=R;j++) if((j&1)==(m>>i&1))
        {
            k=NV*NV+(j-NV*NV>>1);
            dp[e][k]=max(dp[e][k],dp[t][j]);
            tl=min(tl,k);tr=max(tr,k);
        }
        L=tl;R=tr;
    }
    if((m>>41)+NV*NV<L || (m>>41)+NV*NV>R || dp[e][(m>>41)+NV*NV]<inf)
        {puts("impossible");return 0;}
    printf("%lld\n",dp[e][(m>>41)+NV*NV]-inf+a[n]);
}
//#define dxx
#ifdef dxx
#define dbg(...) fprintf(stderr,__VA_ARGS__)
#define dex(a) dbg(#a"=%lld onL%d infun %s\n",(ll)a,__LINE__,__FUNCTION__)
#include<cstdlib>
#define pause sys##tem("pause")
#define _GLIBCXX_DEBUG
#endif

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>

#define fi first
#define se second
const int NV=300;
using ll=long long;
using std::max;
using std::min;
template<class T> void cmax(T&a,T b){a=max(a,b);}
template<class T> void cmin(T&a,T b){a=min(a,b);}

namespace xm{
    std::vector<int> vc[45];
    ll a[NV*2+5],f[2][NV*NV*2+5];
    void _(){
        ll Len;
        int N;

        scanf("%d%lld",&N,&Len);
        for(int i=0;i<=N*2;++i){
            scanf("%lld",a+i);
            if(i==N) continue;
            for(int j=0;j<=40;++j) if(1ll<<j<=a[i]){
                a[i]-=1ll<<j;
                vc[j].push_back(i-N);
            }
            for(int j=40;~j;--j) if(1ll<<j<=a[i]){
                a[i]-=1ll<<j;
                vc[j].push_back(i-N);
            }
        }

        int cur=0,lst=1,L=NV*NV,R=NV*NV;
        f[0][NV*NV]=1e18;
        for(int i=0,tl,tr;i<=40;++i){
            for(int d:vc[i]){
                cur^=1;
                lst^=1;
                tl=min(L,max(0,L+d));
                tr=max(R,min(NV*NV*2,R+d));
                for(int j=tl;j<L;++j) f[cur][j]=0;
                for(int j=L;j<=R;++j) f[cur][j]=f[lst][j];
                for(int j=R+1;j<=tr;++j) f[cur][j]=0;
                for(int j=L,k;j<=R;++j){
                    k=j+d;
                    if(0<=k&&k<=NV*NV*2)
                        cmax(f[cur][k],f[lst][j]+(1ll<<i));
                }
                L=tl;
                R=tr;
            }
            cur^=1;
            lst^=1;
            tl=NV*NV;
            tr=NV*NV;
            for(int j=L;j<=R;++j) f[cur][j]=0;
            for(int j=L,k;j<=R;++j) if((j&1)==(Len>>i&1)){
                k=NV*NV+(j-NV*NV>>1);
                cmax(f[cur][k],f[lst][j]);
                cmin(tl,k);
                cmax(tr,k);
            }
            L=tl;
            R=tr;
        }

        if((Len>>41)+NV*NV<L||(Len>>41)+NV*NV>R||f[cur][(Len>>41)+NV*NV]<ll(1e18))
            puts("impossible");
        else printf("%lld\n",ll(f[cur][(Len>>41)+NV*NV]-ll(1e18)+a[N]));
    }
}

int main(){
    xm::_();
    return 0;
}

answer.code: In function ‘int main()’:
answer.code:37:29: error: no matching function for call to ‘min(int, long long int)’
   37 |             int tr=max(R,min(2*NV*NV,R+d));
      |                          ~~~^~~~~~~~~~~~~
In file included from /usr/include/c++/13/vector:62,
                 from answer.code:2:
/usr/include/c++/13/bits/stl_algobase.h:233:5: note: candidate: ‘template<class _Tp> constexpr const _Tp& std::min(const _Tp&, const _Tp&)’
  233 |     min(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/13/bits/stl_algobase.h:233:5: note:   template argument deduction/substitution failed:
answer.code:37:29: note:   deduced conflicting types for parameter ‘const _Tp’ (‘int’ and ‘long long int’)
   37 |             int tr=max(R,min(2*NV*NV,R+d));
      |                          ~~~^~~~~~~~~~~~~
/usr/include/c++/13/bits/stl_algobase.h:281:5: note: candidate: ‘template<class _Tp, class _Compare> constexpr const _Tp& std::min(const _Tp&, const _Tp&, _Compare)’
  281 |     min(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/13/bits/stl_algobase.h:281:5: note:   template argument deduction/substitution failed:
answer.code:37:29: note:   deduced conflicting types for parameter ‘const _Tp’ (‘int’ and ‘long long int’)
   37 |             int tr=max(R,min(2*NV*NV,R+d));
      |                          ~~~^~~~~~~~~~~~~
/usr/include/strings.h: At global scope:
answer.code:6:18: error: ‘long long long’ is too long for GCC
    6 | #define int long long
      |                  ^~~~
answer.code:6:13: error: ‘long long long’ is too long for GCC
    6 | #define int long long
      |             ^~~~
answer.code:6:18: error: ‘long long long’ is too long for GCC
    6 | #define int long long
      |                  ^~~~
/usr/include/c++/13/bits/uniform_int_dist.h: In member function ‘std::uniform_int_distribution<_IntType>::result_type std::uniform_int_distribution<_IntType>::operator()(_UniformRandomBitGenerator&, const param_type&)’:
answer.code:6:18: error: ‘long long long’ is too long for GCC
    6 | #define int long long
      |                  ^~~~
answer.code:6:18: error: ‘long long long’ is too long for GCC
    6 | #define int long long
      |                  ^~~~
/usr/include/c++/13/bits/stl_algo.h: In function ‘void std::__final_insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare)’:
answer.code:6:13: error: expected primary-expression before ‘long’
    6 | #define int long long
      |             ^~~~
In file included from /usr/include/c++/13/algorithm:61,
                 from answer.code:71:
/usr/include/c++/13/bits/stl_algo.h:1857:29: error: expected ‘)’ before ‘long’
 1857 |       if (__last - __first > int(_S_threshold))
      |          ~                  ^
      |                             )
answer.code:6:13: error: expected primary-expression before ‘long’
    6 | #define int long long
      |             ^~~~
/usr/include/c++/13/bits/stl_algo.h:1859:51: error: expected ‘)’ before ‘long’
 1859 |           std::__insertion_sort(__first, __first + int(_S_threshold), __comp);
      |                                ~                  ^
      |                                                   )
answer.code:6:13: error: expected primary-expression before ‘long’
    6 | #define int long long
      |             ^~~~
/usr/include/c++/13/bits/stl_algo.h:1860:52: error: expected ‘)’ before ‘long’
 1860 |           std::__unguarded_insertion_sort(__first + int(_S_threshold), __last,
      |                                          ~         ^
      |                                                    )
/usr/include/c++/13/bits/stl_algo.h: In function ‘void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size, _Compare)’:
answer.code:6:13: error: expected primary-expression before ‘long’
    6 | #define int long long
      |             ^~~~
/usr/include/c++/13/bits/stl_algo.h:1922:32: error: expected ‘)’ before ‘long’
 1922 |       while (__last - __first > int(_S_threshold))
      |             ~                  ^
      |                                )
answer.code:6:13: error: expected primary-expression before ‘long’
    6 | #define int long long
      |             ^~~~
answer.code: At global scope:
answer.code:76:11: error: conflicting declaration ‘const long long int NV’
   76 | const int NV=300;
      |           ^~
answer.code:5:19: note: previous declaration as ‘const int NV’
    5 | const int M = 605,NV=300;
      |                   ^~
answer.code: In function ‘void xm::_()’:
answer.code:90:17: warning: format ‘%d’ expects argument of type ‘int*’, but argument 2 has type ‘long long int*’ [-Wformat=]
   90 |         scanf("%d%lld",&N,&Len);
      |                ~^      ~~
      |                 |      |
      |                 int*   long long int*
      |                %lld
answer.code:110:29: error: no matching function for call to ‘max(int, long long int)’
  110 |                 tl=min(L,max...