#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;
typedef pair<int, int> pi;
typedef pair<ll,ll> pl;
typedef pair<ld,ld> pd;
typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<cd> vcd;
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;
#define FOR(i, a, b) for (int i=a; i<(b); i++)
#define F0R(i, a) for (int i=0; i<(a); i++)
#define FORd(i,a,b) for (int i = (b)-1; i >= a; i--)
#define F0Rd(i,a) for (int i = (a)-1; i >= 0; i--)
#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()
const int MOD = 1000000007;
const ll INF = 1e18;
const int MX = 4000*4000;
template<int SZ> struct DSU {
int par[SZ], sz[SZ];
DSU() {
F0R(i,SZ) par[i] = i, sz[i] = 1;
}
int get(int x) { // path compression
if (par[x] != x) par[x] = get(par[x]);
return par[x];
}
bool unite(int x, int y) { // union-by-rank
x = get(x), y = get(y);
if (x == y) return 0;
if (sz[x] < sz[y]) swap(x,y);
sz[x] += sz[y], par[y] = x;
return 1;
}
};
DSU<MX> D;
int H,W, dist[MX];
string g[4000];
vi adj[MX];
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
cin >> H >> W;
F0R(i,H) cin >> g[i];
F0R(i,H) F0R(j,W-1) if (g[i][j] == g[i][j+1]) D.unite(W*i+j,W*i+j+1);
F0R(i,H-1) F0R(j,W) if (g[i][j] == g[i+1][j]) D.unite(W*i+j,W*(i+1)+j);
F0R(i,H) F0R(j,W-1) if (g[i][j] != g[i][j+1]) {
if (g[i][j] == '.' || g[i][j+1] == '.') continue;
int a = D.get(W*i+j), b = D.get(W*i+j+1);
adj[a].pb(b), adj[b].pb(a);
}
F0R(i,H-1) F0R(j,W) if (g[i][j] != g[i+1][j]) {
if (g[i][j] == '.' || g[i+1][j] == '.') continue;
int a = D.get(W*i+j), b = D.get(W*(i+1)+j);
adj[a].pb(b), adj[b].pb(a);
}
F0R(i,MX) dist[i] = MOD;
int x = D.get(0); dist[x] = 0;
queue<int> q; q.push(x);
int ans = 0;
while (sz(q)) {
int x = q.front(); q.pop();
for (int i: adj[x]) if (dist[i] == MOD) {
dist[i] = dist[x]+1;
ans = max(ans,dist[i]);
q.push(i);
}
}
cout << ans+1;
}
/* Look for:
* the exact constraints (multiple sets are too slow for n=10^6 :( )
* special cases (n=1?)
* overflow (ll vs int?)
* array bounds
*/
