#include <bits/stdc++.h>
#define ll long long
using namespace std;
int dx[] = {0, 0, -1, 1};
int dy[] = {1, -1, 0, 0};
int main(){
ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
int t = 1;
//cin >> t;
while(t--){
int n, m;
cin >> n >> m;
int dist[n][m];
char grid[n][m];
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++){
cin >> grid[i][j];
dist[i][j] = INT_MAX;
}
}
int ans = 0;
deque<pair<int,int>> q;
q.push_front({0, 0});
dist[0][0] = 0;
while(!q.empty()){
pair<int,int> cur = q.front();
q.pop_front();
ans = max(ans, dist[cur.first][cur.second] + 1);
for(int k = 0; k < 4; k++){
int nx = dx[k] + cur.first;
int ny = dy[k] + cur.second;
if(!(nx >= 0 and nx < n and ny >= 0 and ny < m))continue;
if(grid[nx][ny] == '.')continue;
if(grid[nx][ny] != grid[cur.first][cur.second] and dist[nx][ny] > dist[cur.first][cur.second] + 1){
dist[nx][ny] = dist[cur.first][cur.second] + 1;
q.push_back({nx, ny});
}else if(grid[nx][ny] == grid[cur.first][cur.second] and dist[nx][ny] > dist[cur.first][cur.second]){
dist[nx][ny] = dist[cur.first][cur.second];
q.push_front({nx, ny});
}
}
}
cout << ans << '\n';
}
return 0;
}
