#include<bits/stdc++.h>
using namespace std;
#define int long long int
#define all(v) v.begin(),v.end()
#define pb push_back
#define v vector
void solve(){
int n,m; cin >> n >> m;
v<v<char>> grid(n , v(m , '.'));
vector<vector<int>> weights(n , vector <int> (m , 0));
v<pair<int,int>> edges = {{1,0} , {-1 , 0} , {0 , 1} , {0 , -1}};
for (int i =0; i<n; i++){
for (int j = 0; j<m; j++){
char c; cin >> c;
grid[i][j] = c;
}
}
deque <v<int>> q;
q.push_back({0,0});
int ans = 1;
weights[0][0] = 1;
while (q.size()){
v<int> temp= q.front();
int i = temp[0];
int j = temp[1];
ans = max(ans , weights[i][j]);
q.pop_front();
for (auto [x , y] : edges){
int xx = x + i;
int yy = y + j;
if (xx >= 0 && xx <n && yy >=0 && yy<m && grid[xx][yy] != '.' && weights[xx][yy] == 0){
if (grid[xx][yy] == grid[i][j]){
q.push_front({xx, yy});
weights[xx][yy] = weights[i][j];
}
else{
q.push_back({xx,yy});
weights[xx][yy] = weights[i][j] + 1;
}
}
}
}
cout<<ans;
// for (int i = 0; i<n; i++){
// for (int j = 0; j<m; j++){
// cout<<weights[i][j]<<" ";
// }
// cout<<endl;
// }
}
int32_t main(){
// int n; cin >> n;
int n = 1;
for (int i = 0; i<n; i++){
solve();
}
return 0;
}
