#include <iostream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <cstring>
#include <string>
#include <cmath>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
using namespace std;
#define ll long long
#define ull unsigned long long
#define f first
#define s second
#define PB push_back
#define MP make_pair
#define max(a, b) ((a > b)? a : b)
#define min(a, b) ((a < b)? a : b)
const int N = 4e3 + 5;
const int M = 1e9 + 7;
const int INF = 0x3f3f3f3f;
const int xMove[4] = {0, 1, 0, -1};
const int yMove[4] = {1, 0, -1, 0};
int main(){
ios::sync_with_stdio(false);
cin.tie(NULL);
// ifstream cin();
// ofstream cout();
char meadow[N][N];
int h, w;
cin >> h >> w;
for(int i = 0; i < h; i++){
for(int j = 0; j < w; j++){
cin >> meadow[i][j];
}
}
deque<pair<int, int>> q;
int depth[N][N]{0}, ans = 0;
q.push_front(MP(0, 0));
depth[0][0] = 1;
while(!q.empty()){
auto [x, y] = q.front();
q.pop_front();
ans = max(ans, depth[x][y]);
for(int i = 0; i < 4; i++){
int new_x = x + xMove[i];
int new_y = y + yMove[i];
if(new_x < 0 || new_x >= h || new_y < 0 || new_y >= w) continue;
if(meadow[new_x][new_y] == '.') continue;
if(depth[new_x][new_y] != 0) continue;
if(meadow[x][y] == meadow[new_x][new_y]){
depth[new_x][new_y] = depth[x][y];
q.push_front(MP(new_x, new_y));
}else {
depth[new_x][new_y] = depth[x][y] + 1;
q.push_back(MP(new_x, new_y));
}
}
}
cout << ans << endl;
}
