#include <iostream>
#include <vector>
#include <tuple>
#include <queue>
#include <stack>
#include <deque>
#include <set>
#include <map>
#include <cmath>
#include <array>
#include <random>
#include <string>
#include <cassert>
#include <climits>
#include <algorithm>
#include <unordered_set>
#include <unordered_map>
using namespace std;
#define ll long long
#define f first
#define s second
void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(char x) { cerr << '\'' << x << '\''; }
void __print(const char *x) { cerr << '\"' << x << '\"'; }
void __print(const string &x) { cerr << '\"' << x << '\"'; }
void __print(bool x) { cerr << (x ? "true" : "false"); }
template<typename A> void __print(const A &x);
template<typename A, typename B> void __print(const pair<A, B> &p);
template<typename... A> void __print(const tuple<A...> &t);
template<typename T> void __print(stack<T> s);
template<typename T> void __print(queue<T> q);
template<typename T, typename... U> void __print(priority_queue<T, U...> q);
template<typename A> void __print(const A &x) {
bool first = true;
cerr << '{';
for (const auto &i : x) {
cerr << (first ? "" : ","), __print(i);
first = false;
}
cerr << '}';
}
template<typename A, typename B> void __print(const pair<A, B> &p) {
cerr << '(';
__print(p.f);
cerr << ',';
__print(p.s);
cerr << ')';
}
template<typename... A> void __print(const tuple<A...> &t) {
bool first = true;
cerr << '(';
apply([&first] (const auto &...args) { ((cerr << (first ? "" : ","), __print(args), first = false), ...); }, t);
cerr << ')';
}
template<typename T> void __print(stack<T> s) {
vector<T> debugVector;
while (!s.empty()) {
T t = s.top();
debugVector.push_back(t);
s.pop();
}
reverse(debugVector.begin(), debugVector.end());
__print(debugVector);
}
template<typename T> void __print(queue<T> q) {
vector<T> debugVector;
while (!q.empty()) {
T t = q.front();
debugVector.push_back(t);
q.pop();
}
__print(debugVector);
}
template<typename T, typename... U> void __print(priority_queue<T, U...> q) {
vector<T> debugVector;
while (!q.empty()) {
T t = q.top();
debugVector.push_back(t);
q.pop();
}
__print(debugVector);
}
void _print() { cerr << "]\n"; }
template <typename Head, typename... Tail> void _print(const Head &H, const Tail &...T) {
__print(H);
if (sizeof...(T)) cerr << ", ";
_print(T...);
}
#ifdef DEBUG
#define D(...) cerr << "Line: " << __LINE__ << " [" << #__VA_ARGS__ << "] = ["; _print(__VA_ARGS__)
#else
#define D(...)
#endif
int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, 1, 0, -1};
int h, w, dist[4005][4005], ans;
char grid[4005][4005];
queue<pair<int, int>> q;
bool valid(int x, int y) {
if (x < 0 || x >= h || y < 0 || y >= w || grid[x][y] == '.') return false;
return true;
}
void bfs(int sr, int sc) {
fill(&dist[0][0], &dist[0][0] + sizeof(dist) / sizeof(dist[0][0]), 2e9);
dist[sr][sc] = 1;
q.push({sr, sc});
while (!q.empty()) {
int cr = q.front().f, cc = q.front().s;
q.pop();
for (int i = 0, nr, nc; i < 4; i++) {
nr = cr + dx[i];
nc = cc + dy[i];
if (valid(nr, nc)) {
if (grid[nr][nc] == grid[cr][cc]) {
if (dist[nr][nc] > dist[cr][cc]) {
dist[nr][nc] = dist[cr][cc];
q.push({nr, nc});
}
} else {
if (dist[nr][nc] > dist[cr][cc] + 1) {
dist[nr][nc] = dist[cr][cc] + 1;
q.push({nr, nc});
}
}
}
}
}
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
cin >> h >> w;
for (int i = 0; i < h; i++) {
for (int j = 0; j < w; j++) {
cin >> grid[i][j];
}
}
bfs(0, 0);
for (int i = 0; i < h; i++) {
for (int j = 0; j < w; j++) {
if (dist[i][j] < 2e9) {
ans = max(ans, dist[i][j]);
}
}
}
cout << ans << "\n";
}
