#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;
int H,W, dist[4000][4000];
bool done[4000][4000];
string g[4000];
int xd[4] = {0,1,0,-1}, yd[4] = {1,0,-1,0};
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) dist[i][j] = MOD;
deque<int> q; dist[0][0] = 0; q.pb(0);
int ans = 0;
while (sz(q)) {
int x = q.front(); q.pop_front();
int y = x%W; x /= W;
if (done[x][y]) continue;
done[x][y] = 1;
ans = max(ans,dist[x][y]);
F0R(i,4) {
int X = x+xd[i], Y = y+yd[i];
if (X < 0 || X >= H || Y < 0 || Y >= W) continue;
if (g[X][Y] == '.') continue;
if (g[X][Y] == g[x][y]) {
if (dist[X][Y] > dist[x][y]) {
dist[X][Y] = dist[x][y];
q.push_front(W*X+Y);
}
} else {
if (dist[X][Y] > dist[x][y]+1) {
dist[X][Y] = dist[x][y]+1;
q.pb(W*X+Y);
}
}
}
}
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
*/
