#include<bits/stdc++.h>
using namespace std;
void DBG() { cerr << "]\n"; }
template<class H, class... T> void DBG(H h, T... t) {
cerr << h; if(sizeof...(t)) cerr << ", ";
DBG(t...);
}
#ifdef LOCAL
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
#else
#define dbg(...) 0
#endif // LOCAL
#define FOR(i,a,b) for(int i = (a) ; i<(b) ; i++)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for(int i = (b)-1 ; i>=(a) ; i--)
#define R0F(i,a) ROF(i,0,a)
#define each(e,a) for(auto &e : (a))
#define sz(v) (int)(v).size()
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define pb push_back
#define tcT template<class T
#define nl "\n"
using ll = long long;
using vi = vector<int>;
using pi = pair<int,int>;
using str = string;
tcT> using V = vector<T>;
tcT> using pqg = priority_queue<T,vector<T>,greater<T>>;
void setIO(string NAME = "") {
cin.tie(0)->sync_with_stdio(0);
if(sz(NAME)) {
freopen((NAME + ".inp").c_str(),"r",stdin);
freopen((NAME + ".out").c_str(),"w",stdout);
}
}
tcT> bool ckmax(T&a, const T&b) {
return b > a ? a = b, 1 : 0;
}
const int dx[] = {0, -1, 0, 1};
const int dy[] = {-1, 0, 1, 0};
const int MX = 4e3;
int N, M, dist[MX][MX];
str S[MX];
void solve() {
cin>>N>>M;
F0R(i,N) cin>>S[i];
deque<pi> dq;
dist[0][0] = 1;
dq.pb({0,0});
int ans = 0;
while(sz(dq)) {
int x = dq.front().first, y = dq.front().second;
dq.pop_front();
ckmax(ans, dist[x][y]);
F0R(i,4) {
int nx = x + dx[i], ny = y + dy[i];
if(min(nx,ny)>=0 && nx < N && ny<M && !dist[nx][ny] && S[nx][ny] != '.') {
if(S[nx][ny] == S[x][y]) {
dq.push_front({nx,ny});
dist[nx][ny] = dist[x][y];
}
else {
dq.pb({nx,ny});
dist[nx][ny] = dist[x][y] + 1;
}
}
}
}
cout << ans << nl;
}
int main() {
setIO();
int t=1;
//cin>>t;
while(t-->0) {
solve();
}
return 0;
}
