// Author: Samit Maharjan
// Created: 2022-12-28 22:15
#include "bits/stdc++.h"
using namespace std;
//Typedefs
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ld, ld> pd;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<ld> vd;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<pd> vpd;
//Definitions
#define FOR(i, a, b) for(int i = a; i < b; i++)
#define F0R(i, a) for(int i = 0; i < a; i++)
#define FORr(i, a, b) for(int i = b - 1; i >= a ; i--)
#define F0Rr(i, a) for(int i = a - 1; i >= 0; i--)
#define trav(i, x) for (auto &i : x)
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define all(x) x.begin(), x.end()
#define ins insert
#define pcount __builtin_popcount
#define sz(x) (int)x.size()
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
template<class T> bool ckmin(T& a, const T& b) { return b < a ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) { return a < b ? a = b, 1 : 0; }
template<class T> T inv(T a, T b){ return a == 1 ? 1 : ( (T)1 - inv(b % a, a) * b) / a + b; }
template<class T> T binpow(T a, T b){ return b == 0 ? 1 : (b & 1) ? a * binpow(a * a, b >> 1) : binpow(a * a, b >> 1); }
template<class T> T gcd(T a, T b){ return b ? gcd(b, a % b) : a; }
// Debugging
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 T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ", "; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? ", " : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifdef DEBUG
#define dbg(x...) cerr << "\e[93m"<<__func__<<":"<<__LINE__<<" [" << #x << "] = ["; _print(x); cerr << "\e[39m" << endl;
#else
#define dbg(x...)
#endif
const int N = 4000;
int dist[N * N], g[] = {1, 0, -1, 0, 1};
char grid[N + 1][N + 1];
void solve(){
int m, n; cin >> m >> n;
F0R(i, m){
F0R(j, n){
cin >> grid[i][j];
dist[i * n + j] = 0;
}
}
auto check = [&](int x, int y) -> bool{
return x >= 0 && x < m && y >= 0 && y < n;
};
// will have at least one animal
dist[0] = 1;
deque<int> q; q.push_back(0);
int res = 0;
while(!q.empty() ){
int node = q.front(); q.pop_front();
int x = node / n, y = node % n;
res = max(res, dist[node]);
for(int i = 0; i < 4; ++i){
int nx = x + g[i], ny = y + g[i + 1];
if(check(nx, ny) && grid[nx][ny] != '.' && dist[nx * n + ny] == 0){
if(grid[nx][ny] == grid[x][y]){
q.push_front(nx * n + ny);
dist[nx * n + ny] = dist[node];
} else {
q.push_back(nx * n + ny);
dist[nx * n + ny] = dist[node] + 1;
}
}
}
}
cout << res << endl;
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int t = 1;
//cin >> t;
while(t--)
solve();
return 0;
}
