// https://oj.uz/problem/view/BOI13_tracks
#ifndef DEBUG
#pragma GCC optimize("Ofast,unroll-loops")
#endif
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/trie_policy.hpp>
#if defined(DEBUG) && defined(DEBUG_UTIL)
#include "dsa_util.h"
#endif
// clang-format off
using namespace std;
using namespace __gnu_pbds;
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
constexpr int INF = 0x3f3f3f3f;
constexpr ll INFL = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-9;
constexpr int dx[8] = {1, -1, 0, 0, 1, 1, -1, -1};
constexpr int dy[8] = {0, 0, 1, -1, 1, -1, 1, -1};
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
#if __cplusplus < 202002L
template <typename T> int popcount(T x); template <> int popcount(uint x) { return __builtin_popcount(x); } template <> int popcount(ull x) { return __builtin_popcountll(x); }
template <typename T> int countl_zero(T x); template <> int countl_zero(uint x) { return __builtin_clz(x); } template <> int countl_zero(ull x) { return __builtin_clzll(x); }
template <typename T> int countr_zero(T x); template <> int countr_zero(uint x) { return __builtin_ctz(x); } template <> int countr_zero(ull x) { return __builtin_ctzll(x); }
template <typename T> int bit_width(T x) { return numeric_limits<T>::digits - countl_zero(x); }
#endif
template <typename T> int sgn(T x) { return (T(0) < x) - (x < T(0)); }
template <typename T> T randint(T l, T r) { return uniform_int_distribution<T>(l, r)(rng); }
template <typename T> T randf(T l, T r) { return uniform_real_distribution<T>(l, r)(rng); }
template <typename T> int log2if(T x) { return bit_width(x) - 1; }
template <typename T> int log2ic(T x) { return bit_width(x - 1); }
bool inside(int x, int y, int n, int m) { return x >= 0 && x < n && y >= 0 && y < m; }
ll sqdist(const pair<int, int> &p, const pair<int, int> &q) { ll x = p.first - q.first, y = p.second - q.second; return x * x + y * y; }
#if __cplusplus >= 201703L
template <typename T> using min_priority_queue = priority_queue<T, vector<T>, greater<>>;
template <typename T, typename Comp = less<>> using ordered_set = tree<T, null_type, Comp, rb_tree_tag, tree_order_statistics_node_update>;
using pref_trie = trie<string, null_type, trie_string_access_traits<>, pat_trie_tag, trie_prefix_search_node_update>;
template <typename, typename = void> struct is_iterable : false_type {};
template <typename T> struct is_iterable<T, void_t<decltype(declval<T>().begin()), decltype(declval<T>().end())>> : true_type {};
template <> struct is_iterable<string> : false_type {};
template <typename T> constexpr bool is_iterable_v = is_iterable<T>::value;
template <typename T, typename V = enable_if_t<is_iterable_v<T>, typename T::value_type>> ostream &operator<<(ostream &os, const T &t) { for (const V &v : t) os << v << ' '; return os; }
template <typename T, typename U> ostream &operator<<(ostream &os, const pair<T, U> &p) { return os << '(' << p.first << ' ' << p.second << ')'; }
void dbg_header_(const char *f, int l, const char *e) { cout << "\033[35m(" << f << ':' << l << ") \033[1m" << e << ":\033[0m "; }
template <typename T, typename = enable_if_t<!is_iterable_v<T>>> void dbg_(const T &t, const char *f, int l, const char *e) { dbg_header_(f, l, e); cout << "\033[33;1m" << t << "\033[0m" << endl; }
template <typename T, typename V = enable_if_t<is_iterable_v<T> && !is_iterable_v<typename T::value_type>, typename T::value_type>, typename = void> void dbg_(const T &t, const char *f, int l, const char *e) { dbg_header_(f, l, e); cout << "\033[33;1m"; for (const V &v : t) cout << v << ' '; cout << "\033[0m" << endl; }
template <typename T, typename = enable_if_t<is_iterable_v<T> && is_iterable_v<typename T::value_type>, typename T::value_type>, typename = void, typename = void> void dbg_(const T &t, const char *f, int l, const char *e) { dbg_header_(f, l, e); cout << '\n'; for (int i = 0; i < t.size(); i++) cout << "\033[36m" << i << ":\033[33;1m " << t[i] << "\033[0m" << endl; }
#ifdef DEBUG
#define dbg(t) dbg_((t), __func__, __LINE__, #t)
#else
#define dbg(t)
#endif
#endif
// clang-format on
void solve()
{
#ifdef DEBUG
cout << "\033[31;1m======================================================================\033[0m" << endl;
#endif
int h, w;
cin >> h >> w;
vector<string> grid(h);
for (string &s : grid)
cin >> s;
vector d(h, vector<int>(w, INF));
d[0][0] = 0;
deque<pair<int, int>> q;
q.emplace_front(0, 0);
while (!q.empty())
{
auto [x, y] = q.front();
q.pop_front();
for (int i = 0; i < 4; i++)
{
int nx = x + dx[i], ny = y + dy[i];
if (!inside(nx, ny, h, w) || grid[nx][ny] == '.')
continue;
int cost = grid[x][y] == grid[nx][ny] ? 0 : 1;
if (d[x][y] + cost < d[nx][ny])
{
d[nx][ny] = d[x][y] + cost;
if (cost == 0)
q.emplace_front(nx, ny);
else
q.emplace_back(nx, ny);
}
}
}
int ans = 0;
for (int i = 0; i < h; i++)
{
for (int j = 0; j < w; j++)
{
if (d[i][j] != INF)
ans = max(ans, d[i][j]);
}
}
cout << ans + 1 << endl;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int t = 1;
// cin >> t;
while (t--)
solve();
}
