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#include<cstdio>
#include<set>
#include<vector>

#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)
using namespace std;

char c[200][201];
set<vector<unsigned char> > history;
vector<int> graph[200];
int n, b, r;

void move(vector<unsigned char> & miners) {
  set<unsigned char> S;
  for (unsigned char miner : miners) {
    for (int v : graph[miner]) {
      S.insert(v);
    }
  }
  vector<unsigned char> result(S.begin(), S.end());
  miners.swap(result);
}

bool in_bases(vector<unsigned char> & miners) {
  return miners[miners.size() - 1] < b;
}

int main() {
  scanf("%d%d%d", &n , &b, &r);
  REP(i, n) {
    scanf("%s", c[i]);
    REP(j, n) {
      if (c[i][j] == '1') {
        graph[i].push_back(j);
      }
    }
  }
  vector<unsigned char> miners(r);
  REP(i, r) {
    int miner;
    scanf("%d", &miner);
    miners[i] = miner - 1;
  }
  int moves = 0;
  while (!in_bases(miners)) {
    history.insert(miners);
    move(miners);
    moves++;
    if (history.count(miners)) {
      moves = -1;
      break;
    }
  }
  printf("%d\n", moves);
  return 0;
}