#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 4000;
int dx[4]{1, -1, 0, 0}, dy[4]{0, 0, 1, -1};
int n, m;
int depth[MAX_N][MAX_N];
string snow[MAX_N];
bool inside(int x, int y) {
return x > -1 && x < n && y > -1 && y < m && snow[x][y] != '.';
}
int main() {
cin >> n >> m;
for (int i = 0; i < n; i++) {
cin >> snow[i];
}
deque<pair<int, int>> q;
q.push_back({0, 0});
depth[0][0] = 1;
int result = 1;
while (q.size()) {
pair<int, int> cur = q.front();
q.pop_front();
result = max(result, depth[cur.first][cur.second]);
for (int i = 0; i < 4; i++) {
int x = cur.first + dx[i];
int y = cur.second + dy[i];
if (inside(x, y) && depth[x][y] == 0) {
if (snow[x][y] == snow[cur.first][cur.second]) {
depth[x][y] = depth[cur.first][cur.second];
q.push_front({x, y});
} else {
depth[x][y] = depth[cur.first][cur.second] + 1;
q.push_back({x, y});
}
}
}
}
cout << result << endl;
return 0;
}
