#include <iostream>
#include <string>
#include <cstring>
#include <cmath>
#include <vector>
#include <queue>
#include <set>
#include <algorithm>
#include <map>
#include <fstream>
#include <bitset>
#include <unordered_map>
#include <stack>
#include <list>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef map<int, int> mii;
typedef map<int, string> mis;
typedef map<string, int> msi;
typedef set<int> si;
typedef set<ll> sl;
typedef map<ll, ll> mll;
typedef queue<int> qi;
typedef queue<ii> qii;
typedef vector<string> vs;
typedef pair<ll, ll> iil;
typedef priority_queue<int> pqi;
typedef priority_queue<ii> pqii;
typedef priority_queue<ll> pqil;
typedef priority_queue<iil> pqiil;
typedef vector<iil> viil;
typedef vector<vi> vvi;
typedef long double ld;
typedef pair<int, ii> iii;
typedef pair<iil, ll> iiil;
typedef vector<pair<pair<int,int>,int> > viii;
typedef vector<pair<pair<ll,ll>,ll> > viiil;
typedef vector<vl> vvl;
#define pb push_back
#define mp make_pair
#define rep(i, n) for (int i = 0 ; i < n ; i++)
#define rrep(i, m, n) for (int i = m ; i < n ; i++)
#define per(i, n) for (int i = n - 1 ; i >= 0 ; i--)
#define perr(i, m, n) for (int i = n - 1 ; i >= m ; i--)
#define INF 2000000000
ll MOD = 1000000007;
int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, 1, 0, -1};
int vis[4005][4005];
int dist[4005][4005];
void solve() {
int n, m;
cin >> n >> m;
int mat[n][m];
rep(i, n) {
string s;
cin >> s;
rep(j, m) {
mat[i][j] = s[j];
}
}
deque<pair<pair<int, int>, int>> q;
q.push_back({{0, 0}, 0});
rep(i, n) {
rep(j, m) {
dist[i][j] = INF;
}
}
while (q.size()) {
pair<pair<int, int>, int> inf = q.front();
q.pop_front();
int x = inf.first.first;
int y = inf.first.second;
int d = inf.second;
dist[x][y] = min(dist[x][y], d);
vis[x][y] = true;
rep(k, 4) {
int xx = x + dx[k];
int yy = y + dy[k];
if (xx < 0 || xx >= n || yy < 0 || yy >= m) continue;
if (mat[xx][yy] == '.') continue;
if (mat[xx][yy] == mat[x][y]) {
if (d < dist[xx][yy]) {
q.push_front({{xx, yy}, d});
}
}
else {
if (d+1 < dist[xx][yy]) {
q.push_back({{xx, yy}, d+1});
}
}
}
}
int ans = 0;
rep(i, n) {
rep(j, m) {
if (dist[i][j] != INF) {
//cout << dist[i][j] << " ";
ans = max(ans, dist[i][j]);
}
else {
//cout << 0 << " ";
}
}
//cout << endl;
}
cout << ans+1 << endl;
}
void querySolve() {
int t;
cin >> t;
for (int i = 0 ; i < t ; i++) {
solve();
}
}
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
solve();
//querySolve();
}
