#define IOS ios_base::sync_with_stdio(0); cin.tie(0);

 #include <cstdio>//sprintf islower isupper

 #include <cstdlib>//malloc  exit strcat itoa system("cls")

 #include <iostream>//pair

 #include <fstream>

 #include <bitset>

 //#include <map>

 //#include<unordered_map>

 #include <vector>

 #include <stack>

 #include <set>

 #include <string.h>//strstr substr

 #include <string>

 #include <time.h>//srand(((unsigned)time(NULL))); Seed n=rand()%10 - 0~9;

 #include <cmath>

 #include <deque>

 #include <queue>//priority_queue<int, vector<int>, greater<int> > q;//less

 #include <vector>//emplace_back

 //#include <math.h>

 //#include <windows.h>//reverse(a,a+len);// ~ ! ~ ! floor

 #include <algorithm>//sort + unique : sz=unique(b+1,b+n+1)-(b+1);+nth_element(first, nth, last, compare)

 using namespace std;//next_permutation(a+1,a+1+n);//prev_permutation

 #define mem(a,b) memset(a,b,sizeof(a))

 #define fo(a,b,c) for(a=b;a<=c;++a)//register int i

 #define fr(a,b,c) for(a=b;a>=c;--a)

 #define pr printf

 #define sc scanf

 void swapp(int &a,int &b);

 double fabss(double a);

 int maxx(int a,int b);

 int minn(int a,int b);

 int Del_bit_1(int n);

 int lowbit(int n);

 int abss(int a);

 //const long long INF=(1LL<<60);

 const double E=2.718281828;

 const double PI=acos(-1.0);

 const int inf=(<<);

 const double ESP=1e-;

 const int mod=(int)1e9+;

 const int N=(int)1e6+;

 int val[];

 struct node

 {

     int End;

     long long V;

     bitset<> clique;//团

     friend bool operator<(node a,node b)

     {

         return a.V>b.V;

     }

 };

 bitset<> mp[];

 priority_queue<node> q;

 int main()

 {

     int n,k,i,j;

     sc("%d%d",&n,&k);

     for(i=;i<=n;++i)

         sc("%d",&val[i]);

     for(i=;i<=n;++i)

         for(j=;j<=n;++j)

         {

             int t;

             sc("%1d",&t);

             mp[i][j]=t;

         }

     bitset<> temp;

     q.push({,,temp});

     while(!q.empty())

     {

         node now=q.top();q.pop();

         k--;

         if(k==)

         {

             pr("%lld\n",now.V);

             return ;

         }

         for(i=now.End+;i<=n;++i)

         {

             if((now.clique&mp[i])==now.clique)

             {

                 node v=now;

                 v.clique[i]=;

                 v.End=i;

                 v.V+=val[i];

                 q.push(v);

             }

         }

     }

     pr("-1\n");

     return ;

 }

 /**************************************************************************************/

 int maxx(int a,int b)

 {

     return a>b?a:b;

 }

 void swapp(int &a,int &b)

 {

     a^=b^=a^=b;

 }

 int lowbit(int n)

 {

     return n&(-n);

 }

 int Del_bit_1(int n)

 {

     return n&(n-);

 }

 int abss(int a)

 {

     return a>?a:-a;

 }

 double fabss(double a)

 {

     return a>?a:-a;

 }

 int minn(int a,int b)

 {

     return a<b?a:b;

 }