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#include<cstdio>
#include<algorithm>
#include<ctime>
#include<cstring>
#include<iostream>
#include<cstdlib>
#include<cmath>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<bitset>
using namespace std;
typedef long long ll;
typedef double db;
const db pi=acos(-1);
void gn(int &x){
    int sg=1;char c;while(((c=getchar())<'0'||c>'9')&&c!='-');
    if(c=='-')sg=-1,x=0;else x=c-'0';
    while((c=getchar())>='0'&&c<='9')x=x*10+c-'0';
    x*=sg;
}
void gn(ll &x){
    int sg=1;char c;while(((c=getchar())<'0'||c>'9')&&c!='-');
    if(c=='-')sg=-1,x=0;else x=c-'0';
    while((c=getchar())>='0'&&c<='9')x=x*10+c-'0';
    x*=sg;
}
int gcd(int a,int b){return b?gcd(b,a%b):a;}

int n,c,r;
char s[205][205];
int g[205][205];
int a[205];
int b[205];
inline int test(){
	for (int i=c+1;i<=n;i++)if(a[i])return 0;
	return 1;
}
int main()
{
	scanf("%d%d%d",&n,&c,&r);
	for (int i=1;i<=n;i++)scanf("%s",s[i]+1);
	for (int i=1;i<=n;i++)
		for (int j=1;j<=n;j++)g[i][j]=s[i][j]-'0';
	while(r--){
		int x;scanf("%d",&x);
		a[x]=1;
	}
	for (int k=0;k<=1000;k++){
		if(test()){
			printf("%d\n",k);
			return 0;
		}
		for (int i=1;i<=n;i++)b[i]=0;
		for (int i=1;i<=n;i++)if(a[i])
			for (int j=1;j<=n;j++)b[j]|=g[i][j];
		for (int i=1;i<=n;i++)a[i]=b[i];
	}
	printf("-1\n");
	return 0;
}