#include <bits/stdc++.h>
#include <cstdlib>
using namespace std;
using ll = long long;
using str = string;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pll = pair<ll, ll>;
#define FOR(i, l, r) for (int i=l; i<=r; i++)
#define FOR2(i, l, r) for (int i=l; i>=r; i--)
#define ALL(v) v.begin(), v.end()
#define fi first
#define se second
#define ce cout << endl
#define pb push_back
#define pf push_front
#define pob pop_back
#define pof pop_front
#define eb emplace_back
#define ef emplace_front
#define ep emplace
const ll MOD = 998244353;
const int INF = 1e9;
const int LOG = 60;
const double MAX = 1e9;
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};
// north, south, east, weast
void solve() {
int n, m; cin >> n >> m;
vector<vector<char>> meadow (n, vector<char> (m));
FOR(i, 0, n-1) FOR(j, 0, m-1) cin >> meadow[i][j];
function<bool(int x, int y)> inside = [&] (int x, int y) {
return x >= 0 && x < n && y >= 0 && y < m && meadow[x][y] != '.';
};
vector<vector<int>> depth(n, vector<int> (m, -1));
deque<pii> dq;
depth[0][0] = 0;
dq.eb(0, 0);
int res = 0;
while (!dq.empty()) {
auto [x1, y1] = dq.back(); dq.pob();
res = max(res, depth[x1][y1]);
FOR(i, 0, 3) {
int x2 = x1 + dx[i], y2 = y1 + dy[i];
if (!inside(x2, y2) || depth[x2][y2] != -1) continue;
if (meadow[x2][y2] == meadow[x1][y1]) {
depth[x2][y2] = depth[x1][y1];
dq.eb(x2, y2);
} else {
depth[x2][y2] = depth[x1][y1]+1;
dq.ef(x2, y2);
}
}
}
cout << res+1;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
// freopen("movie.in", "r", stdin);
// freopen("movie.out", "w", stdout);
int t = 1;
// cin >> t;
while (t--) solve();
}
