#include <bits/stdc++.h>
using std::vector;
using std::array;
using std::pair;
using std::tuple;
constexpr int inf = std::numeric_limits<int>::max() / 2;
bool setmin(int& x, const int y) {
if (x > y) {
x = y;
return true;
}
return false;
}
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
int N, M;
std::cin >> N >> M;
const int V = (N + 2) * (M + 2);
const auto cell = [&](const int i, const int j) {
return i * (M + 2) + j;
};
vector<char> grid(V, '*');
for (int i = 1; i <= N; ++i) {
for (int j = 1; j <= M; ++j) {
std::cin >> grid[cell(i, j)];
}
}
vector<int> dist(V, inf);
std::deque<int> que;
dist[cell(1, 1)] = 1;
que.push_back(cell(1, 1));
while (!que.empty()) {
const int u = que.front();
que.pop_front();
for (const int v : {u + 1, u - 1, u + (M + 2), u - (M + 2)}) {
if (grid[v] == '*') {
continue;
}
if (grid[u] != grid[v]) {
if (setmin(dist[v], dist[u] + 1)) {
que.push_back(v);
}
} else {
if (setmin(dist[v], dist[u])) {
que.push_front(v);
}
}
}
}
int ans = 0;
for (int i = 0; i < V; ++i) {
if (grid[i] != '*') {
ans = std::max(ans, dist[i]);
}
}
std::cout << ans << '\n';
return 0;
}
