#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES

#include <bits/stdc++.h>
using namespace std;
using i32 = int32_t;  using i64 = int64_t;  using str = string;
using u32 = uint32_t; using u64 = uint64_t; using usize = size_t;
using f64 = double_t; template <typename T> using vec = vector<T>;
#define times(n, i) for (i64 i = 0; i < (n); ++i)
#define range(n, m, i) for (i64 i = (n); i < (m); ++i)
#define upto(n, m, i) for (i64 i = (n); i <= (m); ++i)
#define downto(n, m, i) for (i64 i = (n); i >= (m); --i)
#define foreach(xs, x) for (auto &x : (xs))
#define all(xs) (xs).begin(), (xs).end()
#define sortall(xs) sort(all(xs))
#define reverseall(xs) reverse(all(xs))
#define uniqueall(xs) (xs).erase(unique(all(xs)), (xs).end())
#define maximum(xs) (*max_element(all(xs)))
#define minimum(xs) (*min_element(all(xs)))
#define even(x) (((x) & 1) == 0)
#define odd(x) (((x) & 1) == 1)
#define append emplace_back
const i64 MOD = 1000000007;

i32 h, w;
vec<str> m;
i32 dp[3001][3001];

i32 main()
{
    cin >> h >> w;
    m.resize(h);
    times(h, i) {
        cin >> m[i];
    }

    i32 ans = 0;
    times(h, i) {
        times(w, j) {
            if (m[i][j] == '.')
                dp[i+1][j+1] = 0;
            else
                dp[i+1][j+1] = min(dp[i][j], min(dp[i][j+1], dp[i+1][j])) + 1;
            ans = max(ans, dp[i+1][j+1]);
        }
    }
    
    cout << (ans+1)/2 << endl;
    return 0;
}