#include <bits/stdc++.h>
#include <deque>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define file "test"
#define forr(i, a, b) for (int i = (a), _b = (b); i <= _b; ++i)
#define ford(i, b, a) for (int i = (b), _a = (a); i >= _a; --i)
#define forf(i, a, b) for (int i = (a), _b = (b); i < _b; ++i)
#define rep(i, n) for (int i = 0, _n = (n); i < _n; ++i)
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(x) x.begin(), x.end()
#define MASK(i) (1LL << (i))
#define bit(x, i) (((x) >> (i)) & 1)
#define bp __builtin_popcountll
const int maxn = 4e3 + 10;
const int MOD = 1e9 + 7; // 998244353 // 1e9 + 2277 // 1e9 + 5277
const ll inf = 1e18;
const int oo = 1e9 + 7;
const float eps = 1e-6;
template<class X, class Y>
bool minimize(X &x, const Y &y) {
if (x > y) {
x = y;
return true;
}
return 0;
}
template<class X, class Y>
bool maximize(X &x, const Y &y) {
if (x < y) {
x = y;
return true;
}
return 0;
}
/* END OF TEMPLATE. WHAT A SIGMA! TAKE A DEEP BREATH AND READY FOR CODING :D */
int h, w, d[maxn][maxn], ans;
int dx[] = {-1, 0, 1, 0};
int dy[] = {0, 1, 0, -1};
char a[maxn][maxn];
bool ok(int x, int y) {
return x >= 1 && x <= h && y >= 1 && y <= w && a[x][y] != '.';
}
void bfs(int i, int j) {
deque<pii> q;
q.push_back(mp(i, j));
d[i][j] = 1;
while (q.size()) {
pii curr = q.front();
q.pop_front();
ans = max(ans, d[curr.fi][curr.se]);
forf(k, 0, 4) {
int newi = curr.fi + dx[k];
int newj = curr.se + dy[k];
if (ok(newi, newj) && !d[newi][newj]) {
if (a[i][j] == a[newi][newj]) {
d[newi][newj] = d[i][j];
q.push_front(mp(newi, newj));
}
else {
d[newi][newj] = d[i][j] + 1;
q.push_back(mp(newi, newj));
}
}
}
}
cout << ans;
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
#ifndef ONLINE_JUDGE
freopen(file".inp", "r", stdin);
freopen(file".out", "w", stdout);
#endif
cin >> h >> w;
forr(i, 1, h)
forr(j, 1, w)
cin >> a[i][j];
bfs(1, 1);
return 0;
}
