#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair<int,int>
const int maxn = 2100;
char g[maxn][maxn];
int vis[maxn][maxn], dist[maxn][maxn];
int dX[] = {0, 1, 0, -1};
int dY[] = {1, 0, -1, 0};
int32_t main() {
ios_base::sync_with_stdio(false); cin.tie(0);
int h, w; cin >> h >> w;
for (int i = 1; i <= h; i++)
for (int j = 1; j <= w; j++)
cin >> g[i][j];
deque<pii> dq;
dq.push_front({1, 1});
int ans = 0;
while(!dq.empty()) {
int x = dq.front().first, y = dq.front().second;
dq.pop_front();
vis[x][y] = true;
ans = max(ans, dist[x][y]);
for (int i = 0; i < 4; i++) {
int curX = x + dX[i], curY = y + dY[i];
if(curX < 1 || curX > h || curY < 1 || curY > w) continue;
if(vis[curX][curY]) continue;
if(g[curX][curY] == g[x][y]) {
dq.push_front({curX, curY});
dist[curX][curY] = dist[x][y];
}
else {
dq.push_back({curX, curY});
dist[curX][curY] = dist[x][y] + 1;
}
}
}
cout << ans << '\n';
}
