// #include <bits/stdc++.h>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <map>
#include <vector>
#include <iomanip>
#include <string>
#include <queue>
#include <set>
#include <deque>
#include <numeric>
#include <stack>
#include <chrono>
using namespace std;
#define int long long
#define endl '\n'
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define fi first
#define se second
const int N = 4005;
int n, m, dist[N][N];
bool vis[N][N];
string s[N];
vector<int> dx = {0, 0, 1, -1}, dy = {1, -1, 0, 0};
bool check(int x, int y){
return (x > 0 && x <= n && y > 0 && y <= m && !vis[x][y] && s[x][y] != '.');
}
signed bfs(){
priority_queue<pair<int, pair<int, int>>, vector<pair<int, pair<int, int>>>, greater<pair<int, pair<int, int>>>> q;
q.push({1, {1, 1}});
vis[1][1] = 1;
int ma = 0;
while (q.size()){
auto [D, coord] = q.top(); q.pop();
auto [x, y] = coord;
// cout << x << ' ' << y << endl;
ma = max(ma, D);
for (auto ddx : dx){
for (auto ddy : dy){
int cx = x + ddx, cy = y + ddy;
if (check(cx, cy) && s[cx][cy] == s[x][y]){
dist[cx][cy] = D;
q.push({dist[cx][cy], {cx, cy}});
vis[cx][cy] = 1;
}
else if (check(cx, cy)){
dist[cx][cy] = D + 1;
q.push({dist[cx][cy], {cx, cy}});
vis[cx][cy] = 1;
}
}
}
}
return ma;
}
void solve() {
cin >> n >> m;
for (int i = 1; i <= n; i++){
cin >> s[i];
s[i] = "." + s[i];
}
for (int i = 1; i <= n; i++){
for (int j = 1; j <= m; j++) dist[i][j] = 1e18;
}
dist[1][1] = 1;
cout << bfs() << endl;
return;
}
signed main() {
srand(chrono::steady_clock::now().time_since_epoch().count());
int tc = 1;
// cin >> tc;
while (tc--) solve();
return 0;
}
