// This template is based on - Baltic OI 2013 - Tracks in the Snow
// this is basically dijstra, but seems pretty dang cool
#include <bits/stdc++.h>
#define ll long long
using namespace std;
int dx[4] = {0, 0, 1, -1};
int dy[4] = {-1, 1, 0, 0};
signed main(){
cin.tie(0) -> sync_with_stdio(0);
int h, w;
cin >> h >> w;
vector<vector<char>> board(h+5, vector<char>(w+5));
vector<vector<int>> level(h+5, vector<int>(w+5, -1));
for (int i = 1; i <= h; i++){
for (int j = 1; j <= w; j++){
cin >> board[i][j];
}
}
deque<pair<int, int>> q;
q.push_back({1, 1});
level[1][1] = 1;
int ans = 0;
while (!q.empty()){
pair<int, int> u = q.front();
q.pop_front();
int x = u.first, y = u.second;
ans = max(ans, level[y][x]);
for (int k = 0; k < 4; k++){
int tx = x + dx[k], ty = y + dy[k];
if (tx <= 0 || ty <= 0 || tx > w || ty > h || board[ty][tx] == '.' || level[ty][tx] != -1) continue;
if (board[y][x] == board[ty][tx]){
level[ty][tx] = level[y][x];
q.push_front({tx, ty});
}
else{
level[ty][tx] = level[y][x] + 1;
q.push_back({tx, ty});
}
}
}
cout << ans;
}
