#include<bits/stdc++.h>
using namespace std;
#define ll long long int
// #define ll double
#define vl vector<ll>
#define vpll vector<pair<ll,ll>>
#define vvl vector<vector<ll>>
#define vvc vector<vector<char>>
#define newl cout << endl;
#define dbg(v) cout << "Line(" << __LINE__ << ") -> " << #v << " = " << (v) << endl;
const ll N = 4*(1e3) + 2;
// vvl adj(N);
vector<string> field(N);
// vector<ll> vis(N,0);
ll n, m;
ll dr[4] = {+1, 0, 0, -1};
ll dc[4] = {0, -1, +1, 0};
bool check(ll r, ll c){
if(r < 0 || r >= n) return false;
if(c < 0 || c >= m) return false;
if(field[r][c] == '.') return false;
return true;
}
void solve(){
cin >> n >> m;
for(ll i = 0; i < n; i++){
cin >> field[i];
}
deque<pair<ll,ll>> q;
vvl dist(n, vl(m, -1));
q.push_back({0,0});
dist[0][0] = 1;
ll ans = 1;
while(!q.empty()){
auto it = q.front();
q.pop_front();
ll r = it.first;
ll c = it.second;
for(ll i = 0; i < 4; i++){
ll nr = r + dr[i];
ll nc = c + dc[i];
ans = max(ans , dist[r][c]);
if(!check(nr, nc)) continue;
if(dist[nr][nc] == -1){
if(field[r][c] == field[nr][nc]){
dist[nr][nc] = dist[r][c];
q.push_front({nr, nc});
}
else{
dist[nr][nc] = dist[r][c] + 1;
q.push_back({nr, nc});
// ans++;
}
}
}
}
cout << ans << endl;
return;
}
int main(){
ll t=1;
// cin>>t;
while(t>0){
solve();
t--;
}
return 0;
}
