// #pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
#define el "\n"
#define pii pair<int, int>
#define pll pair<ll, ll>
#define fi first
#define se second
#define sqr(x) ((x) * (x))
#define FOR(i, l, r) for (int i = l; i <= (r); i++)
#define FOD(i, l, r) for (int i = l; i >= (r); i--)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) ((int)(x).size())
#define fast_io ios_base::sync_with_stdio(false); cin.tie(nullptr);
using db = long double;
using ll = long long;
using ull = unsigned long long;
using vi = vector<int>;
using vll = vector<ll>;
using vpii = vector<pii>;
using vpll = vector<pll>;
using vvi = vector<vi>;
using vvll = vector<vll>;
using vbool = vector<bool>;
using vvbool = vector<vbool>;
template<class T> inline bool chmax(T &a, T const &b) { return (a < b ? (a = b, true) : false); }
template<class T> inline bool chmin(T &a, T const &b) { return (a > b ? (a = b, true) : false); }
// #define DEBUG
#ifdef DEBUG
#include "D:\cpp\debug.h"
#else
#define debug(...)
#define debug_arr(...)
#endif
mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count());
constexpr int N = 4E3 + 5;
constexpr int INF = 1E9 + 7;
constexpr ll INFLL = 4E18;
constexpr int MOD = 1E9 + 7; // 998244353
constexpr double EPS = 1E-10;
int H, W;
char grid[N][N];
int d[N][N];
constexpr int DIRECTIONS[4][2] = {{-1, 0}, {+1, 0}, {0, -1}, {0, +1}};
void solve() {
cin >> H >> W;
FOR(i, 1, H) {
FOR(j, 1, W) {
cin >> grid[i][j];
}
}
if (grid[1][1] == '.') {
cout << 0 << el;
return;
}
deque<pii> dq;
memset(d, 0x3f, sizeof d);
dq.emplace_front(1, 1);
d[1][1] = 1;
int res = 1;
while (!dq.empty()) {
auto [x, y] = dq.front();
chmax(res, d[x][y]);
dq.pop_front();
for (auto &[dx, dy] : DIRECTIONS) {
int nx = x + dx, ny = y + dy;
if (nx < 1 || nx > H || ny < 1 || ny > W || grid[nx][ny] == '.') continue;
if (grid[nx][ny] == grid[x][y] && chmin(d[nx][ny], d[x][y])) {
dq.emplace_front(nx, ny);
}
if (grid[nx][ny] != grid[x][y] && chmin(d[nx][ny], d[x][y] + 1)) {
dq.emplace_back(nx, ny);
}
}
}
cout << res << el;
}
int main() {
fast_io
#define LOCAL
#ifndef LOCAL
#define PROBLEM "tracks"
freopen(PROBLEM ".in", "r", stdin);
freopen(PROBLEM ".out", "w", stdout);
#endif
int t = 1;
// cin >> t;
while (t--) solve();
}
