#include <bits/stdc++.h>
using namespace std;
int main() {
int n, m;
cin >> n >> m;
vector<vector<char>> meadow(n, vector<char>(m));
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
cin >> meadow[i][j];
}
}
vector<vector<int>> d(n, vector<int>(m));
vector<vector<int>> used(n, vector<int>(m));
deque<pair<int, int>> q;
q.push_front({0, 0});
used[0][0] = true;
d[0][0] = 1;
while (!q.empty()) {
auto [r, c] = q.front();
q.pop_front();
static vector<pair<int, int>> dirs = {{-1, 0}, {0, 1}, {1, 0}, {0, -1}};
for (auto [x, y] : dirs) {
x += r, y += c;
if (x >= 0 && x < n && y >= 0 && y < m && !used[x][y] &&
meadow[x][y] != '.') {
if (meadow[r][c] != meadow[x][y]) {
d[x][y] = d[r][c] + 1;
q.push_back({x, y});
} else {
d[x][y] = d[r][c];
q.push_front({x, y});
}
used[x][y] = true;
}
}
}
int rv = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
rv = max(rv, d[i][j]);
}
}
cout << rv << "\n";
}
