#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using pii = pair<int, int>;
#define pb push_back
#define sz(x) (int)(x).size()
#define f first
#define s second
#define mp make_pair
const int INF = INT_MAX;
const int MOD = 1e9 + 7;
const int hmx = 4005, wmx = 4005;
int h, w, ans = 1;
vector<string> grid(hmx);
vector<vi> depth(hmx, vi (wmx));
int dx[]{0, 1, 0, -1}, dy[]{1, 0, -1, 0};
bool is_valid(int r, int c) {
return r >= 0 && r < h && c >= 0 && c < w && grid[r][c] != '.';
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> h >> w;
for (int i = 0; i < h; i++)
cin >> grid[i];
deque<pair<int, int>> dq;
dq.push_front({0, 0});
depth[0][0] = 1;
while (!dq.empty()) {
auto nxt = dq.front();
dq.pop_front();
ans = max(ans, depth[nxt.f][nxt.s]);
for (int i = 0; i < 4; i++) {
int x = nxt.f + dx[i], y = nxt.s + dy[i];
if (is_valid(x, y) && depth[x][y] == 0) {
if (grid[x][y] == grid[nxt.f][nxt.s]) {
depth[x][y] = depth[nxt.f][nxt.s];
dq.push_front({x, y});
} else {
depth[x][y] = depth[nxt.f][nxt.s] + 1;
dq.push_back({x, y});
}
}
}
}
cout << ans << "\n";
return 0;
}
