#include <bits/stdc++.h>
using namespace std;
using ll = int64_t;
constexpr array<int, 4> dx = {1, 0, -1, 0}, dy = {0, 1, 0, -1};
int main() {
ios::sync_with_stdio(false); cin.tie(nullptr);
int n, m; cin >> n >> m;
vector<string> grid(n);
for (string &s: grid) cin >> s;
function<bool(int, int)> isValid = [&] (int x, int y) {
return 0 <= x and x < n and 0 <= y and y < m and grid[x][y] != '.';
};
int ans = 0;
vector<vector<int>> dist(n, vector<int>(m, -1));
dist[0][0] = 1;
deque<array<int, 2>> q; // {x, y}
q.push_back({0, 0});
while (not q.empty()) {
auto [x0, y0] = q.front(); q.pop_front();
ans = max(ans, dist[x0][y0]);
for (int i = 0; i < 4; i++) {
int x = x0 + dx[i], y = y0 + dy[i];
if (not isValid(x, y) or dist[x][y] != -1) continue;
if (grid[x][y] != grid[x0][y0]) {
dist[x][y] = dist[x0][y0] + 1;
q.push_back({x, y});
} else {
dist[x][y] = dist[x0][y0];
q.push_front({x, y});
}
}
}
cout << ans;
return 0;
}
