#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
void DBG() { cerr << "]" << endl; }
template<class H, class... T> void DBG(H h, T... t) { cerr << to_string(h); if(sizeof...(t)) cerr << ", "; DBG(t...); }
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
const int N = 4003;
char a[N][N];
bool vis[N][N];
const int POM[4][2] = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
void solve() {
int n, m; cin >> n >> m;
deque<tuple<int, int, int, char>> pq;
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++) cin >> a[i][j];
pq.push_back({1, n, m, a[n][m]});
int ans = 1;
while (!pq.empty()) {
auto [w, i, j, c] = pq.front(); pq.pop_front();
if (vis[i][j]) continue;
ans = max(ans, w);
vis[i][j] = true;
for (int d = 0; d < 4; d++) {
int ik = i + POM[d][0], jk = j + POM[d][1];
if (ik < 1 || ik > n || jk < 1 || jk > m) continue;
if (vis[ik][jk] || a[ik][jk] == '.') continue;
char c2 = a[ik][jk];
if (c != c2)
pq.push_back({w + 1, ik, jk, c2});
else
pq.push_front({w, ik, jk, c2});
}
}
cout << ans << "\n";
}
signed main() {
ios::sync_with_stdio(false); cin.tie(0);
int t=1; //cin >> t;
while (t--) {
solve();
}
}
