#define MOD_TYPE 2 #include using namespace std; #include // #include // #include // #include using namespace atcoder; #if 0 #include #include using Int = boost::multiprecision::cpp_int; using lld = boost::multiprecision::cpp_dec_float_100; #endif #if 0 #include #include #include #include using namespace __gnu_pbds; using namespace __gnu_cxx; template using extset = tree, rb_tree_tag, tree_order_statistics_node_update>; #endif #if 1 #pragma GCC target("avx2") #pragma GCC optimize("O3") #pragma GCC optimize("unroll-loops") #endif #pragma region Macros using ll = long long int; using ld = long double; using pii = pair; using pll = pair; using pld = pair; template using smaller_queue = priority_queue, greater>; #if MOD_TYPE == 1 constexpr ll MOD = ll(1e9 + 7); #else #if MOD_TYPE == 2 constexpr ll MOD = 998244353; #else constexpr ll MOD = 1000003; #endif #endif using mint = static_modint; constexpr int INF = (int)1e9 + 10; constexpr ll LINF = (ll)4e18; const double PI = acos(-1.0); constexpr ld EPS = 1e-10; constexpr int Dx[] = {0, 0, -1, 1, -1, 1, -1, 1, 0}; constexpr int Dy[] = {1, -1, 0, 0, -1, -1, 1, 1, 0}; #define REP(i, m, n) for (ll i = m; i < (ll)(n); ++i) #define rep(i, n) REP(i, 0, n) #define REPI(i, m, n) for (int i = m; i < (int)(n); ++i) #define repi(i, n) REPI(i, 0, n) #define RREP(i, m, n) for (ll i = n - 1; i >= m; i--) #define rrep(i, n) RREP(i, 0, n) #define YES(n) cout << ((n) ? "YES" : "NO") << "\n" #define Yes(n) cout << ((n) ? "Yes" : "No") << "\n" #define all(v) v.begin(), v.end() #define NP(v) next_permutation(all(v)) #define dbg(x) cerr << #x << ":" << x << "\n"; #define UNIQUE(v) v.erase(unique(all(v)), v.end()) struct io_init { io_init() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << setprecision(20) << setiosflags(ios::fixed); }; } io_init; template inline bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; } template inline bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; } inline ll floor(ll a, ll b) { if (b < 0) a *= -1, b *= -1; if (a >= 0) return a / b; return -((-a + b - 1) / b); } inline ll ceil(ll a, ll b) { return floor(a + b - 1, b); } template inline void Fill(A (&array)[N], const T &val) { fill((T *)array, (T *)(array + N), val); } template vector compress(vector &v) { vector val = v; sort(all(val)), val.erase(unique(all(val)), val.end()); for (auto &&vi : v) vi = lower_bound(all(val), vi) - val.begin(); return val; } template constexpr istream &operator>>(istream &is, pair &p) noexcept { is >> p.first >> p.second; return is; } template constexpr ostream &operator<<(ostream &os, pair p) noexcept { os << p.first << " " << p.second; return os; } ostream &operator<<(ostream &os, mint m) { os << m.val(); return os; } ostream &operator<<(ostream &os, modint m) { os << m.val(); return os; } template constexpr istream &operator>>(istream &is, vector &v) noexcept { for (int i = 0; i < v.size(); i++) is >> v[i]; return is; } template constexpr ostream &operator<<(ostream &os, vector &v) noexcept { for (int i = 0; i < v.size(); i++) os << v[i] << (i + 1 == v.size() ? "" : " "); return os; } template constexpr void operator--(vector &v, int) noexcept { for (int i = 0; i < v.size(); i++) v[i]--; } random_device seed_gen; mt19937_64 engine(seed_gen()); inline ll randInt(ll l, ll r) { return engine() % (r - l + 1) + l; } struct BiCoef { vector fact_, inv_, finv_; BiCoef(int n) noexcept : fact_(n, 1), inv_(n, 1), finv_(n, 1) { fact_.assign(n, 1), inv_.assign(n, 1), finv_.assign(n, 1); for (int i = 2; i < n; i++) { fact_[i] = fact_[i - 1] * i; inv_[i] = -inv_[MOD % i] * (MOD / i); finv_[i] = finv_[i - 1] * inv_[i]; } } mint C(ll n, ll k) const noexcept { if (n < k || n < 0 || k < 0) return 0; return fact_[n] * finv_[k] * finv_[n - k]; } mint P(ll n, ll k) const noexcept { return C(n, k) * fact_[k]; } mint H(ll n, ll k) const noexcept { return C(n + k - 1, k); } mint Ch1(ll n, ll k) const noexcept { if (n < 0 || k < 0) return 0; mint res = 0; for (int i = 0; i < n; i++) res += C(n, i) * mint(n - i).pow(k) * (i & 1 ? -1 : 1); return res; } mint fact(ll n) const noexcept { if (n < 0) return 0; return fact_[n]; } mint inv(ll n) const noexcept { if (n < 0) return 0; return inv_[n]; } mint finv(ll n) const noexcept { if (n < 0) return 0; return finv_[n]; } }; BiCoef bc(1000010); #pragma endregion // ------------------------------- void solve() { int h, w; cin >> h >> w; vector s(h); cin >> s; vector csum(h + 1, vector(w + 1)); rep(i, h) rep(j, w) { csum[i + 1][j + 1] = (s[i][j] == '#') + csum[i + 1][j] + csum[i][j + 1] - csum[i][j]; } // a[li][lj]を含み,a[ri][rj]を含まない auto csumf = [&](int li, int lj, int ri, int rj) { return csum[ri][rj] - csum[li][rj] - csum[ri][lj] + csum[li][lj]; }; auto simulate = [&](int k) { vector imos(h + 1, vector(w + 1)); rep(i, h - k + 1) rep(j, w - k + 1) { if (csumf(i, j, i + k, j + k) == k * k) { imos[i][j]++; imos[i + k][j]--; imos[i][j + k]--; imos[i + k][j + k]++; } } rep(i, h) rep(j, w) imos[i][j + 1] += imos[i][j]; rep(j, w) rep(i, h) imos[i + 1][j] += imos[i][j]; rep(i, h) rep(j, w) { if ((imos[i][j] > 0) != (s[i][j] == '#')) return false; } return true; }; auto binary_search = [&]() { int lo = 0, hi = min(h, w) + 1; while (hi - lo > 1) { ll mi = (lo + hi) / 2; if (simulate(mi)) lo = mi; else hi = mi; } return lo; }; cout << binary_search() << "\n"; } int main() { solve(); }