#include<cstdio>

#include<algorithm>

#include<bitset>

#include<queue>

using namespace std;

typedef long long LL;

typedef bitset<> BS;

struct node{

    LL sum;

    int pos;

    BS vis;

    node(){}

    node(LL s,int p,BS v){

        this->sum=s;

        this->pos=p;

        this->vis=v;

    }

    bool operator < (const node& other) const{

        return sum>other.sum;

    }

};

int n,k;

LL a[];

BS b[];

char s[];

int main(){

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

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

        scanf("%lld",&a[i]);

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

        scanf("%s",s);

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

            b[i][j]=s[j-]-'';

    }

    BS tmp;

    tmp.reset();

    priority_queue<node> pq;

    pq.push(node(,,tmp));

    while(!pq.empty()){

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

        if(--k==){

            printf("%lld\n",now.sum);

            return ;

        }

        for(int i=now.pos;i<=n;++i)

            if((b[i]&now.vis)==now.vis){

                now.vis[i]=;

                pq.push(node(now.sum+a[i],i+,now.vis));

                now.vis[i]=;

            }

    }

    printf("-1\n");

    return ;

}