#pragma GCC target("avx2")
#pragma GCC optimize("unroll-loops")

#include <algorithm>
#include <bitset>
#include <climits>
#include <cmath>
#include <cstring>
#include <deque>
#include <forward_list>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

#define ALL(x) (x).begin(), (x).end()
#define PC(x) __builtin_popcount(x)
#define PCL(x) __builtin_popcountll(x)

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
struct edge {
    int to, cost, id;
};
const double PI = 3.14159265358979323846;
const double PI2 = PI * 2.0;
const double EPS = 1E-09;
const ll MOD = 1E+09 + 7; // =998244353;
const ll INFL = 1E18;
const int INFI = 1E09;
const int MAX_N = 3E+03;

ll dx[4] = { -1, 1, 0, 0 }, dy[4] = { 0, 0, -1, 1 };

int H, W, dp[MAX_N + 1][MAX_N + 1];

bool S[MAX_N + 1][MAX_N + 1];

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    cin >> H >> W;

    for (int i = 1; i <= H; ++i) {
        for (int j = 1; j <= W; ++j) {
            char c;
            cin >> c;
            if (c == '#')
                S[i][j] = true;
        }
    }
    for (int i = 1; i <= H; ++i) {
        for (int j = 1; j <= W; ++j) {
            if (S[i][j]) {
                dp[i][j] = min({ dp[i - 1][j],
                               dp[i][j - 1],
                               dp[i - 1][j - 1] })
                    + 1;
            }
        }
    }
    int ans = 0;
    for (int i = 1; i <= H; ++i) {
        for (int j = 1; j <= W; ++j) {
            ans = max(ans, dp[i][j] / 2 + 1);
        }
    }

    // for (int i = 0; i < N; i++) {
    //     for (int j = 0; j < N; j++) {
    //         cout << "i = " << i << ", j = " << j << ", dp = " << dp[i][j] << "\n";
    //     }
    // }
    cout << ans << "\n";

    return 0;
}