//0/1 bfs each element, find max
#include <iostream>
#include <queue>
using namespace std;
using pii = pair<int, int>;
int h,w, ans=1;
string field[4001];
bool used[4001][4001];
pii dir[4] = {{0,1},{1,0},{-1,0},{0,-1}};
pii operator+(pii a, pii b){
return make_pair(a.first+b.first, a.second+b.second);
}
deque<pii> q;
deque<int> moves;
deque<char> sign;
bool out(pii a){
if (a.first < 0 || a.second < 0 || a.first > h || a.second > w) return true;
return false;
}
int main(){
cin >> h >> w;
for (int i=0; i<h; i++){
cin >> field[i];
}
q.push_back({0,0});
moves.push_back(1);
sign.push_back(field[0][0]);
used[0][0] = true;
while (!q.empty()){
pii cur = q.front(); q.pop_front();
int curmove = moves.front(); moves.pop_front();
char cursign = sign.front(); sign.pop_front();
ans = max(ans, curmove);
for (int i=0; i<4; i++){
pii newp = cur + dir[i];
if (out(newp) || field[newp.first][newp.second] == '.' || used[newp.first][newp.second]) continue;
if (field[newp.first][newp.second] == cursign){
sign.push_front(cursign);
moves.push_front(curmove);
q.push_front(newp);
}
else{
sign.push_back(field[newp.first][newp.second]);
moves.push_back(curmove+1);
q.push_back(newp);
}
used[newp.first][newp.second] = true;
}
}
cout << ans;
}
