#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define pii pair<int, int>
#define sz size
#define st first
#define nd second
const int N = 4010;
const int inf = 1e9 + 3;
int h, w;
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};
int dis[N][N];
bool vis[N][N];
char tab[N][N];
int ans;
void bfs(int x = 1, int y = 1){
priority_queue<pair<int, pii>> q;
vis[x][y] = 1;
dis[x][y] = 1;
q.push({1, {x, y}});
while (!q.empty()){
auto v = q.top();
q.pop();
int sx = v.nd.st, sy = v.nd.nd;
ans = max(dis[sx][sy], ans);
vis[sx][sy] = 1;
for (int i = 0; i < 4; i ++){
int nx = sx + dx[i], ny = sy + dy[i];
if (nx < 1 || ny < 1 || nx > h || ny > w) continue;
if (vis[nx][ny]) continue;
if (tab[nx][ny] == '.') continue;
if (tab[nx][ny] == tab[sx][sy]){
dis[nx][ny] = min(dis[sx][sy], dis[nx][ny]);
q.push({-1 * dis[nx][ny], {nx, ny}});
}
if (tab[nx][ny] != tab[sx][sy]){
dis[nx][ny] = min(dis[sx][sy] + 1, dis[nx][ny]);
q.push({-1 * dis[nx][ny], {nx, ny}});
}
}
}
}
void cl(){
for (int i = 0; i < N; i ++){
for (int j = 0; j < N; j ++){
dis[i][j] = inf;
}
}
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cl();
cin >> h >> w;
for (int i = 1; i <= h; i ++){
for (int j = 1; j <= w; j ++){
cin >> tab[i][j];
}
}
bfs();
cout << ans << "\n";
}
