#include<bits/stdc++.h>
using namespace std;
#define r first
#define c second
int n,m;
const int maxn = 4100;
string grid[maxn];
int d[maxn][maxn];
int ans = 1;
//UDLR
int dr[] = {1,-1,0,0};
int dc[] = {0,0,-1,1};
bool check(pair<int,int> u){
return u.r >= 0 && u.r < n && u.c >= 0 && u.c < m && grid[u.r][u.c] != '.';
}
void dfs(pair<int,int> s){
d[s.r][s.c] = 1;
deque<pair<int,int>> next;
next.push_front(s);
while(!next.empty()){
pair<int,int> u = next.front();
next.pop_front();
ans = max(ans,d[u.r][u.c]);
// cerr << "(r,c): " << u.r << " " << u.c << " d: " << d[u.r][u.c] << "\n";
for(int i = 0;i < 4;++i){
pair<int,int> v = {u.r + dr[i],u.c + dc[i]};
if(check(v) && d[v.r][v.c] == 0){
if(grid[u.r][u.c] == grid[v.r][v.c]){
d[v.r][v.c] = d[u.r][u.c];
next.push_front(v);
} else {
d[v.r][v.c] = d[u.r][u.c] + 1;
next.push_back(v);
}
}
}
}
}
int main(){
cin >> n >> m;
for(int i = 0;i < n;++i){
cin >> grid[i];
}
memset(d,0,sizeof(d));
dfs({0,0});
cout << ans << "\n";
return 0;
}
