#include <iostream>
#include <algorithm>
#include <utility>
#include <vector>
#include <queue>
using namespace std;
const int N = 4000;
int n, m, region[N][N], ans = 1;
string snow[N];
int dx[4]{1, -1, 0, 0}, dy[4]{0, 0, 1, -1};
bool valid(int x, int y) {
return (x >= 0 && x < n && y >= 0 && y < m && snow[x][y] != '.');
}
int main() {
iostream::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> m;
for (int i = 0; i < n; i++) cin >> snow[i];
deque<pair<int, int>> Q;
Q.push_back({0, 0});
region[0][0] = 1;
while (!Q.empty()) {
auto [x, y] = Q.front();
Q.pop_front();
ans = max(ans, region[x][y]);
for (int i = 0; i < 4; i++) {
int nx = x + dx[i];
int ny = y + dy[i];
if (!valid(nx, ny) || region[nx][ny]) continue;
if (snow[nx][ny] == snow[x][y]) {
region[nx][ny] = region[x][y];
Q.push_front({nx, ny});
} else {
region[nx][ny] = region[x][y] + 1;
Q.push_back({nx, ny});
}
}
}
cout << ans << endl;
return 0;
}
