#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
#define ordered_set <int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
#define ordered_multiset <int, null_type, less_equal <int>, rb_tree_tag, tree_order_statistics_node_update>
#define int long long
#define double long double
#define pii pair <int, int>
#define tiii tuple <int, int, int>
#define tiiii tuple <int, int, int, int>
#define emb emplace_back
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define iShowSpeed cin.tie(NULL)->sync_with_stdio(false)
#define matrix vector <vector <int>>
#define mat(n, m) vector <vector <int>> (n, vector <int> (m));
const int mod = 1e9 + 7;
const int inf = 1e18;
const matrix II = {{1, 0}, {0, 1}};
void solve(){
int n, m; cin >> n >> m;
char a[n + 1][m + 1];
for (int i = 1; i <= n; i++) for (int j = 1; j <= m; j++) cin >> a[i][j];
deque <pii> q; q.emplace_front(1, 1);
int dis[n + 1][m + 1]; memset(dis, 0, sizeof dis); dis[1][1] = 1;
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
int ans = 0;
while (!q.empty()) {
auto [x, y] = q.front(); q.pop_front();
for (int i = 0; i < 4; i++) {
int nx = x + dx[i], ny = y + dy[i];
if (nx < 1 || nx > n || ny < 1 || ny > m || a[nx][ny] == '.' || dis[nx][ny] > 0) continue;
if (a[x][y] != a[nx][ny]) q.emplace_back(nx, ny);
else q.emplace_front(nx, ny);
dis[nx][ny] = dis[x][y] + (a[x][y] != a[nx][ny]);
// if (a[x][y] != a[nx][ny]) cout << x << ' ' << y << "\n";
ans = max(ans, dis[nx][ny]);
}
}
cout << ans;
}
int32_t main(){
iShowSpeed;
// int q; cin >> q; while (q--)
solve();
}
