#include <bits/stdc++.h>
using namespace std;
const int maxn = 4010;
char c[maxn][maxn];
int d[maxn][maxn];
int dx[] = {-1,1,0,0};
int dy[] = {0,0,-1,1};
bool vis[maxn][maxn];
int n,m;
bool check(int x,int y){
return (x >= 1 && x <= n && y >= 1 && y <= m && c[x][y] != '.' && !vis[x][y]);
}
void bfs(){
vis[1][1] = true;
int ans = 0;
deque<pair<int,int>> q;
q.push_front({1,1});
d[1][1] = 1;
while(!q.empty()){
pair<int,int> u = q.front();
q.pop_front();
ans = max(ans,d[u.first][u.second]);
for(int k = 0 ; k < 4; k++){
int xx = u.first + dx[k];
int yy = u.second + dy[k];
if(check(xx,yy)){
if(c[u.first][u.second] == c[xx][yy]){
vis[xx][yy] = true;
d[xx][yy] = d[u.first][u.second];
q.push_front({xx,yy});
}
else {
vis[xx][yy] = true;
d[xx][yy] = d[u.first][u.second] + 1;
q.push_back({xx,yy});
}
}
}
}
cout << ans << endl;
}
int main(){
cin >> n >> m;
for(int i =1; i<= n ;i++){
for(int j = 1 ; j <= m ;j ++) cin >> c[i][j];
}
bfs();
}
