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#include <bits/stdc++.h>

using namespace std;

const int N = 205;

int n, b, r;
int maxi[305];
bool vis[305][N];
char slowo[N][N];
int graf[N][N];
queue<pair<int, int> >Q;
int gornik[N];

int main() {
    
    scanf("%d %d %d", &n, &b, &r);
    
    for (int i = 1; i <= n; i++) {
        scanf("%s", &slowo[i][1]);
        for (int j = 1; j <= n; j++) {
            graf[i][j] = slowo[i][j] - 48;
        }
    }
    
    for (int i = 1; i <= r; i++) {
        scanf("%d", &gornik[i]);
        vis[0][gornik[i]] = true;
        Q.push({gornik[i], 0});
        maxi[0] = gornik[i];
    }
    
    while(!Q.empty()) {
        int w = Q.front().first;
        int dl = Q.front().second;
        if (maxi[dl] <= b) {
            printf("%d\n", dl);
            exit(0);
        }
        Q.pop();
        if (dl > 301) {
            break;
        }
        for (int i = 1; i <= n; i++) {
            if (graf[w][i] && vis[dl + 1][i] == false) {
                vis[dl + 1][i] = true;
                maxi[dl + 1] = max(maxi[dl + 1], i);
                Q.push({i, dl + 1});
            }
        }
    }
    
    printf("-1\n");
    return 0;
}