#include <bits/stdc++.h>
using namespace std;
char grid[4000][4000];
int H, W, dist[4000][4000];
const int dx[4] = {0,0,1,-1}, dy[4] = {1,-1,0,0}, mx = 1e9;
int main(){
cin >> H >> W;
for(int i=0;i<H;i++){
for(int j=0;j<W;j++){
cin >> grid[i][j];
dist[i][j] = mx;
}
}
deque<pair<int,int>> d;
dist[0][0] = 1;
d.push_back({0,0});
int ans = 0;
while(!d.empty()){
pair<int,int> curr = d.front();
d.pop_front();
ans = max(ans, dist[curr.first][curr.second]);
for(int i=0;i<4;i++){
int x = curr.first + dx[i], y = curr.second + dy[i];
if(x >= 0 && x < H && y >= 0 && y < W && grid[x][y] != '.'){
int w = grid[x][y] == grid[curr.first][curr.second] ? 0:1;
if(dist[curr.first][curr.second] + w < dist[x][y]){
dist[x][y] = dist[curr.first][curr.second] + w;
if(w == 0) d.push_front({x,y});
else d.push_back({x,y});
}
}
}
}
cout << ans << "\n";
return 0;
}
