#include <iostream>
#include <bitset>
#include <vector>
#include <string>
#include <sstream>
#include <algorithm>
#include <set>
#include <map>
#include <stack>
#include <cmath>
#include <regex>
#include <iomanip>
#include <climits>
#include <utility>
#include <queue>
#include <numeric>
#include <time.h>
using namespace std;
using ll = long long int;
using dd = long double;
const ll MOD = 1e9 + 7;
const dd PI = 3.1415926435;

class UnionFind
{
public:
    UnionFind(int N) : par(N)
    {
        for (ll i = 0; i < N; i++)
        {
            par[i] = i;
        }
    }

    int root(int x)
    {
        if (par[x] == x)
            return x;
        return par[x] = root(par[x]);
    }

    void unite(int x, int y)
    {
        int rx = root(x);
        int ry = root(y);
        if (rx == ry)
            return;
        par[rx] = ry;
    }

    bool same(int x, int y)
    {
        int rx = root(x);
        int ry = root(y);
        return rx == ry;
    }

private:
    vector<int> par;
};

ll gcd(ll a, ll b)
{
    if (a % b == 0)
    {
        return b;
    }
    return gcd(b, a % b);
}

ll fact(ll n)
{
    if (n <= 0)
    {
        return 1;
    }
    if (n == 1)
    {
        return 1;
    }
    return n * fact(n - 1) % MOD;
}

ll pow_fast(ll n, ll k)
{
    if (k == 0)
    {
        return 1;
    }
    if (k == 1)
    {
        return n;
    }

    if (k % 2 == 0)
    {
        ll tmp = pow_fast(n, k / 2LL);
        return tmp * tmp % MOD;
    }
    else
    {
        ll tmp = pow_fast(n, k / 2LL);
        tmp *= tmp;
        tmp %= MOD;
        return tmp * n % MOD;
    }
}

map<ll, ll> sosuu(ll n)
{
    map<ll, ll> res;
    for (ll i = 2; i * i <= n; i++)
    {
        while (n % i == 0)
        {
            res[i] += 1;
            n /= i;
        }
    }
    if (n != 1)
    {
        res[n] += 1;
    }
    return res;
}

struct Dish
{
    ll time;
    ll taste;
};

static ll FACTORIAL[10000010] = {};
ll nCk(ll n, ll k)
{
    if (FACTORIAL[1] == 0)
    {
        FACTORIAL[0] = 1;
        FACTORIAL[1] = 1;
        for (ll i = 2; i <= 10000000; i++)
        {
            FACTORIAL[i] = FACTORIAL[i - 1] * i;
            FACTORIAL[i] %= MOD;
        }
    }
    ll N_fact = FACTORIAL[n];
    ll K_fact = pow_fast(FACTORIAL[k], MOD - 2);
    ll N_K_fact = pow_fast(FACTORIAL[n - k], MOD - 2);
    ll ret = N_fact;
    ret %= MOD;
    ret *= K_fact;
    ret %= MOD;
    ret *= N_K_fact;
    ret %= MOD;
    return ret;
}

void solve(string s, ll K)
{
    ll sum = 0;
    for (ll i = s.size(); i <= s.size() + K; i++)
    {
        // 25
        ll cnt = pow_fast(25, i - s.size()) % MOD;
        cnt *= nCk(i - 1, s.size() - 1);
        cnt %= MOD;

        // 26
        cnt *= pow_fast(26, s.size() + K - i);
        cnt %= MOD;

        sum += cnt;
        sum %= MOD;
    }
    cout << sum << endl;
    return;
}

vector<string> explode(string s, char delim)
{
    vector<string> ret;
    string cur;
    for (ll i = 0; i < s.size(); i++)
    {
        if (s[i] == delim)
        {
            ret.push_back(cur);
            cur.clear();
            continue;
        }
        cur += s[i];
    }

    if (cur.size() != 0)
    {
        ret.push_back(cur);
    }

    return ret;
}

template <typename T>
void DEBUG(T var)
{
    static size_t cnt = 1;
    cout << "[DEBUG] " << cnt << " :";
    cout << "(" << typeid(var).name() << ")";
    cout << var << endl;
    cnt += 1;
}

struct Element
{
    char c;
    bool visited;
    ll cost;
};

vector<vector<ll>> comb(ll n)
{
    vector<vector<ll>> ans(n + 1, vector<ll>(n + 1));

    ans[0][0] = 0;

    for (ll i = 1; i <= n; i++)
    {
        for (ll j = 0; j <= i; j++)
        {
            if (j == 0 || j == i)
            {
                ans[i][j] = 1;
                continue;
            }
            ans[i][j] = ans[i - 1][j] + ans[i - 1][j - 1];
        }
    }

    return ans;
}

int main()
{
    ll H, W;
    cin >> H >> W;

    vector<vector<char>> mp(H, vector<char>(W));
    for (ll i = 0; i < H; i++)
    {
        string S;
        cin >> S;
        for (ll j = 0; j < W; j++)
        {
            mp[i][j] = S[j];
        }
    }

    vector<vector<ll>> cost(H, vector<ll>(W, INT_MAX));
    auto solved = [&cost](ll H, ll W) {
        bool ok = true;
        for (ll i = 0; i < H; i++)
        {
            for (ll j = 0; j < W; j++)
            {
                if (cost[i][j] == INT_MAX)
                {
                    ok = false;
                }
            }
        }
        return ok;
    };

    for (ll i = 0; i < H; i++)
    {
        for (ll j = 0; j < W; j++)
        {
            if (mp[i][j] == '#')
            {
                cost[i][j] = 0;
            }
        }
    }

    while (!solved(H, W))
    {
        for (ll i = 0; i < H; i++)
        {
            ll next = INT_MAX;
            for (ll j = 0; j < W; j++)
            {
                ll cur = min(cost[i][j], next);
                if (cur == INT_MAX)
                {
                    continue;
                }
                cost[i][j] = cur;
                next = cur + 1;
            }

            next = INT_MAX;
            for (ll j = W - 1; j >= 0; j--)
            {
                ll cur = min(cost[i][j], next);
                if (cur == INT_MAX)
                {
                    continue;
                }
                cost[i][j] = cur;
                next = cur + 1;
            }
        }

        for (ll j = 0; j < W; j++)
        {
            ll next = INT_MAX;
            for (ll i = 0; i < H; i++)
            {
                ll cur = min(cost[i][j], next);
                if (cur == INT_MAX)
                {
                    continue;
                }
                cost[i][j] = cur;
                next = cur + 1;
            }

            next = INT_MAX;
            for (ll i = H - 1; i >= 0; i--)
            {
                ll cur = min(cost[i][j], next);
                if (cur == INT_MAX)
                {
                    continue;
                }
                cost[i][j] = cur;
                next = cur + 1;
            }
        }
    }

    ll ans = 0;
    for (ll i = 0; i < H; i++)
    {
        for (ll j = 0; j < W; j++)
        {
            ans = max(ans, cost[i][j]);
        }
    }
    cout << ans << endl;
}


Measured memory_bytes: 12176