#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int,int>;
using ld = long double;
#define el cout << '\n'
#define fi first
#define se second
#define pb push_back
#define all(x) x.begin(), x.end()
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#define FOD(i, a, b) for (int i = (a); i >= (b); i--)
#define REP(i, n) for (int i = 0; i < (n); i++)
template <class T1, class T2>bool chmax(T1 &a, T2 b){if (a < b) {a = b; return true;}return false;}
template <class T1, class T2>bool chmin(T1 &a, T2 b){if (a > b) {a = b; return true;}return false;}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const ll mod = 1e9 + 7;
const int maxn = 5e5 + 5;
void solve(){
int h, w;
cin >> h >> w;
string s[h];
REP(i, h){
cin >> s[i];
cerr << s[i] << endl;
}
vector<vector<int>> dep(h, vector<int> (w));
int dx[4] = {0, 0, -1, 1};
int dy[4] = {-1, 1, 0, 0};
deque<pii> dq;
dq.push_back({0, 0});
dep[0][0] = 1;
int ans = 1;
while(dq.size()){
auto [a, b] = dq.front();
dq.pop_front();
chmax(ans, dep[a][b]);
for (int i = 0; i < 4; i++){
int x = a + dx[i];
int y = b + dy[i];
if (x < 0 || x >= h || y < 0 || y >= w) continue;
if (s[x][y] == '.' || dep[x][y] != 0) continue;
if (s[x][y] == s[a][b]){
dep[x][y] = dep[a][b];
dq.push_front({x, y});
}
else{
dep[x][y] = dep[a][b] + 1;
dq.push_back({x, y});
}
}
}
cout << ans;
}
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int tests = 1;
//cin >> tests;
for (int _ = 1; _ <= tests; _++){
cerr << "- Case #" << _ << ": \n";
solve();
el;
}
return 0;
}
