#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair<int,int>
const int maxn = 4100;
string g[maxn];
int dist[maxn][maxn];
int dx[4]{1, -1, 0, 0}, dy[4]{0, 0, 1, -1};
int h, w;
bool inside(int x, int y) {
return (x > -1 && x < h && y > -1 && y < w && g[x][y] != '.');
}
int32_t main() {
ios_base::sync_with_stdio(false); cin.tie(0);
cin >> h >> w;
for (int i = 0; i < h; i++)
cin >> g[i];
deque<pii> dq;
dist[0][0] = 1;
dq.push_front({0, 0});
int ans = 0;
while (dq.size()) {
pair<int, int> c = dq.front();
dq.pop_front();
ans = max(ans, dist[c.first][c.second]);
for (int i = 0; i < 4; i++) {
int x = c.first + dx[i], y = c.second + dy[i];
if (inside(x, y) && dist[x][y] == 0) {
if (g[x][y] == g[c.first][c.second]) {
dist[x][y] = dist[c.first][c.second];
dq.push_front({x, y});
} else {
dist[x][y] = dist[c.first][c.second] + 1;
dq.push_back({x, y});
}
}
}
}
cout << ans << '\n';
}
