#include <bits/stdc++.h>
    #include <ext/pb_ds/assoc_container.hpp>
    #include <ext/pb_ds/tree_policy.hpp>

    using namespace std;
    using namespace __gnu_pbds;

    template <typename T>
    using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

    typedef long long ll;
    typedef pair<ll, ll> pll;
    typedef pair<int, int> pii;
    typedef complex<double> point;

    #define X real()
    #define Y imag()
    #define angle(a) (atan2((a).imag(), (a).real()))
    #define vec(a, b) ((b) - (a))
    #define same(p1, p2) (dp(vec(p1, p2), vec(p1, p2)) < EPS)
    #define dp(a, b) ((conj(a) * (b)).real())
    #define cp(a, b) ((conj(a) * (b)).imag())
    #define length(a) (hypot((a).imag(), (a).real()))
    #define normalize(a) (a) / length(a)
    #define rotateO(p, ang) ((p)*exp(point(0, ang)))
    #define rotateA(p, ang, about) (rotateO(vec(about, p), ang) + about)
    #define reflectO(v, m) (conj((v) / (m)) * (m))

    const ll N = 1005;
    const int MOD = 1e5;
    const double EPS = 1e-5;
    const double PI = acos(-1.0);

    int dx[] = {-1, 0, 0, 1};
    int dy[] = {0, -1, 1, 0};

    ll n, m, mat[N][N], dist[N][N];

    bool valid(ll x, ll y)
    {
        return x >= 0 && x < n && y >= 0 && y < m && mat[x][y] == 1;
    }

    int main()
    {
        scanf("%lld %lld", &n, &m);

        queue<pll> Q;

        memset(dist, -1, sizeof(dist));

        for(int i = 0; i < n; i++)
            for(int j = 0; j < m; j++)
            {
                scanf("%lld", &mat[i][j]);
                if(mat[i][j] == 2)
                {
                    Q.push({i, j});
                    dist[i][j] = 0;
                }
            }

        while(!Q.empty())
        {
            ll x = Q.front().first;
            ll y = Q.front().second;
            Q.pop();

            for(int i = 0; i < 4; i++)
            {
                ll nx = x + dx[i];
                ll ny = y + dy[i];
                if(valid(nx, ny) && (dist[nx][ny] == -1 || dist[nx][ny] > dist[x][y] + 1))
                {
                    dist[nx][ny] = dist[x][y] + 1;
                    Q.push({nx, ny});
                }
            }
        }
        ll maxx = 0;
        for(int i = 0; i < n; i++)
         for(int j = 0; j < m; j++)
            if(mat[i][j] == 1)
            {
                if(dist[i][j] == -1)
                {
                    printf("-1\n");
                    return 0;
                }
                else
                    maxx = max(maxx, dist[i][j]);
            }
        printf("%lld\n", maxx);
    }