#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pi pair<int,int>
int32_t main(){
int n,m; cin >> n >> m;
string s[n];
for(int i=0; i<n; i++){
cin >> s[i];
}
vector <pi> v = {{1,0},{0,1},{-1,0},{0,-1}};
if(s[0][0]=='.'){cout << 0 << endl; return 0;}
int ans = 1;
vector <vector<bool>> vis(n,vector<bool>(m,0));
vis[0][0] = 1;
deque <pi> q;
q.push_front({0,0});
vector <vector<int>> d(n,vector<int>(m,0));
d[0][0] = 1;
function <bool(int,int)> ok = [&](int x,int y){
if(x<0 || x>n-1 || y<0 || y>m-1){return false;}
if(vis[x][y]){return false;}
return (s[x][y] != '.');
};
function <void(pi)> process = [&](pi k){
for(auto e:v){
int x = e.first+k.first;
int y = e.second+k.second;
if(ok(x,y)){
vis[x][y] = 1;
d[x][y] = d[k.first][k.second];
if(s[x][y] != s[k.first][k.second]){
q.push_back({x,y});
d[x][y]++;
}else{
q.push_front({x,y});
}
}
}
};
while(q.size()){
auto k = q.front();
q.pop_front();
ans = max(ans,d[k.first][k.second]);
process(k);
}
cout << ans << endl;
}
