/*=======================================
Build : LOCAL / Debug
Compiler : g++ -std=gnu++17
Note: read problem twice ฅ(^>⩊<^) ฅ
=======================================*/
#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#define _GLIBCXX_DEBUG
#include "debug.hpp"
#else
#define debug(...) ((void)0)
#endif
#define sz(v) ((int)((v).size()))
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
using ll = int64_t;
using db = long double;
const int mxN = (int)4e3+5;
const int xdir[4]{1,0,-1,0}, ydir[4]{0,1,0,-1};
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;
template<typename T> int lwb(const vector<T>& a, const T& x){
return lower_bound(a.begin(), a.end(), x) - a.begin(); }
template<typename T> int upb(const vector<T>& a, const T& x){
return upper_bound(a.begin(), a.end(), x) - a.begin(); }
constexpr int pct(int x) { return __builtin_popcount(x); } // # of bits set
constexpr int ctz(int x) { // assert(x >= 0);
return x == 0 ? -1 : __builtin_ctz(x); } // # of trailing zeros
constexpr int bits(int x) { // assert(x >= 0);
return x == 0 ? 0 : 31-__builtin_clz(x); } // floor(log2(x))
template<typename T> bool ckmin(T& a, const T& b) { return b < a ? a = b, 1 : 0; }
template<typename T> bool ckmax(T& a, const T& b) { return a < b ? a = b, 1 : 0; }
int n, m;
char g[mxN][mxN];
int dist[mxN][mxN];
bool valid(int x, int y) {
return g[x][y] != '.';
}
void bfs(int sx, int sy) {
deque<pair<int,int>> todo;
todo.push_front({sx, sy});
dist[sx][sy] = 1;
while (sz(todo)) {
auto [x, y] = todo.front(); todo.pop_front();
for (int i = 0; i < 4; i++) {
int nx = x + xdir[i];
int ny = y + ydir[i];
if (nx < 0 || nx >= n || ny < 0 || ny >= m) continue;
if(!valid(nx, ny)) continue;
if(g[nx][ny] == g[x][y]) {
if(ckmin(dist[nx][ny], dist[x][y]))
todo.push_front({nx, ny});
} else {
if(ckmin(dist[nx][ny], dist[x][y]+1))
todo.push_back({nx, ny});
}
}
}
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> m;
memset(dist, 0x3f, sizeof(dist));
for(int i = 0; i < n; ++i)
for(int j = 0; j < m; ++j) {
cin >> g[i][j];
if(g[i][j] == '.')
dist[i][j] = -1;
}
bfs(0, 0);
int ans = 0;
for(int i = 0; i < n; ++i)
for(int j = 0; j < m; ++j) {
ckmax(ans, dist[i][j]);
}
cout << ans;
return 0;
}
