#include <iostream>
#include <queue>
using namespace std;
typedef pair<int, int> pii;
#define mp make_pair
#define ff first
#define ss second
int n, m;
char grid[4007][4007];
int depth[4007][4007];
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};
bool chk(int x, int y) {
return (x > -1 && x < n && y > -1 && y < m && grid[x][y] != '.');
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n >> m;
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++)
cin >> grid[i][j];
}
int ans = 1;
deque<pii> q;
q.push_back(mp(0, 0));
depth[0][0] = 1;
while(q.size()){
pii u = q.front();
q.pop_front();
ans = max(ans, depth[u.ff][u.ss]);
for(int i = 0; i < 4; i++){
int x = u.ff + dx[i], y = u.ss + dy[i];
if(chk(x, y) && depth[x][y] == 0){
if(grid[x][y] == grid[u.ff][u.ss]){
depth[x][y] = depth[u.ff][u.ss];
q.push_front(mp(x, y));
}else{
depth[x][y] = depth[u.ff][u.ss] + 1;
q.push_back(mp(x, y));
}
}
}
}
cout << ans << endl;
return 0;
}
