#pragma GCC optimize ("O3")
#include <bits/stdc++.h>
//#include<ext/pb_ds/assoc_container.hpp>
//#include<ext/pb_ds/tree_policy.hpp>
#define pii pair<int, int>
#define piii pair<pii, int>
#define vi vector<int>
#define vll vector<ll>
#define vvi vector<vi>
#define vpii vector<pii>
#define vvpii vector<vpii>
#define f first
#define s second
#define oo 1000000001
#define eb emplace_back
#define pb push_back
#define mpr make_pair
#define size(v) (int)v.size()
#define ln '\n'
#define ull unsigned long long
#define ll long long
#define all(v) v.begin(), v.end()
#define iospeed ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0)
//#define pbase 361549
//#define imod 1073737591
//#define uimod 2147479307u
//#define llmod 292187309552789533ll
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
//using namespace __gnu_pbds;
//template <typename T>
//using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template <typename T>
void show(vector<T> &v) {
for (T i : v) {
cout << i << ' ';
}
cout << ln;
}
int dx[] = {1, -1, 0, 0};
int dy[] = {0, 0, 1, -1};
void solve() {
int h, w;
cin >> h >> w;
vector<string>s(h);
for (string &r : s) {
cin >> r;
}
deque<array<int, 2>>q;
vvi dist(h, vi(w, 0));
q.push_back({0, 0});
dist[0][0] = 1;
int res = 1;
while (!q.empty()) {
auto [x, y] = q.front();
res = max(res, dist[x][y]);
q.pop_front();
for (int i = 0; i < 4; ++i) {
int nx = x + dx[i];
int ny = y + dy[i];
if (nx >= 0 && nx < h && ny >= 0 && ny < w && !dist[nx][ny] && s[nx][ny] != '.') {
dist[nx][ny] = dist[x][y];
if (s[nx][ny] == s[x][y]) {
q.push_front({nx, ny});
} else {
++dist[nx][ny];
q.push_back({nx, ny});
}
}
}
}
cout << res << ln;
}
int main() {
iospeed;
solve();
return 0;
}
