#include <bits/stdc++.h>
using namespace std;
int n, m, depth[4001][4001];
int dx[] = {1, -1, 0, 0};
int dy[] = {0, 0, 1, -1};
char grid[4001][4001];
bool inside(int i, int j){
if(i < 0 || i >= n || j < 0 || j >= m || grid[i][j] == '.') return false;
else return true;
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> m;
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++){
cin >> grid[i][j];
}
}
depth[0][0] = 1;
deque<pair<int, int>> q;
q.push_back({0, 0});
int ans = 0;
while(!q.empty()){
auto s = q.front();
q.pop_front();
int x = s.first;
int y = s.second;
ans = max(ans, depth[x][y]);
for(int i = 0; i < 4; i++){
int sx = x + dx[i];
int sy = y + dy[i];
if(inside(sx, sy) && depth[sx][sy] == 0){
if(grid[x][y] == grid[sx][sy]){
depth[sx][sy] = depth[x][y];
q.push_front({sx, sy});
}else{
depth[sx][sy] = depth[x][y] + 1;
q.push_back({sx, sy});
}
}
}
}
cout << ans << endl;
return 0;
}
