#include<bits/stdc++.h>
using namespace std;
#define int int
#define double double
const int INF = INT_MAX-10;
const int NINF = -INF;
const int MOD = 998244353;
int dx[4]{-1, 1, 0, 0}, dy[4]{0, 0, -1, 1};
const int maxH = 4005, maxW = 4005;
string grid[maxH];
int dist[maxH][maxW];
int H, W;
bool inside(int x, int y) {
return x >= 0 && y >= 0 && x < H && y < W && grid[x][y] != '.';
}
int ans = 0;
void solve() {
cin >> H >> W;
for(int i=0; i<H; i++) {
cin >> grid[i];
}
deque<pair<int, int>> dq;
dq.push_back({0,0});
dist[0][0] = 1;
while(!dq.empty()) {
pair<int, int> a = dq.front();
dq.pop_front();
ans = max(ans, dist[a.first][a.second]);
for(int i=0; i<4; i++) {
int x = a.first + dx[i], y = a.second + dy[i];
if(inside(x, y) && dist[x][y] == 0) {
if(grid[x][y] == grid[a.first][a.second]) {
dist[x][y] = dist[a.first][a.second];
dq.push_front({x, y});
} else {
dist[x][y] = dist[a.first][a.second] + 1;
dq.push_back({x, y});
}
}
}
}
cout << ans << "\n";
}
int32_t main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
cout << fixed << setprecision(10);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
return 0;
}
