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#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <fstream>
#include <sstream>
#include <set>
#include <map>
#include <vector>
#include <list>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <string>
#include <queue>
#include <bitset>		//UWAGA - w czasie kompilacji musi byc znany rozmiar wektora - nie mozna go zmienic
#include <cassert>
#include <iomanip>		//do setprecision
#include <ctime>
#include <complex>
using namespace std;

#define FOR(i,b,e) for(int i=(b);i<(e);++i)
#define FORQ(i,b,e) for(int i=(b);i<=(e);++i)
#define FORD(i,b,e) for(int i=(b)-1;i>=(e);--i)
#define REP(x, n) for(int x = 0; x < (n); ++x)

#define ST first
#define ND second
#define PB push_back
#define MP make_pair
#define LL long long
#define ULL unsigned LL
#define LD long double

const double pi = 3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342;

#define MR 210

int t[2][MR];
char g[MR][MR];

int treshold = 1e4;
int done[MR];

int main()
{
	int n, b, r;
	scanf("%d%d%d", &n, &b, &r);
	REP(i,n) scanf("%s", g[i]);
	REP(i,r)
	{
		int a;
		scanf("%d", &a);a--;
		t[0][i] = a;
	}

	bool sel = 0;
	REP(c,treshold)
	{
		bool ok = 1;
		REP(i,r)
			if(t[sel][i] >= b)
			{
				ok = 0;
				break;
			}
		if(ok)
		{
			printf("%d\n", c);
			return 0;
		}
		int r1 = 0;
		REP(i,r)REP(j,n)
			if(g[t[sel][i]][j] == '1' && done[j] != c+1)
			{
				t[!sel][r1++] = j;
				done[j] = c+1;
			}

		r = r1;
		sel = !sel;
	}

	printf("-1\n");
	return 0;
}