#include <bits/stdc++.h>
#define int long long
#pragma GCC optimize("O3")
#define vi vector<int>
#define vb vector<bool>
#define F(i, s, e) for(int i = s; i < e; i++)
#define sp <<' '<<
#define pii pair<int, int>
#define fi first
#define se second
#define pb push_back
#define vvi vector<vi>
#define vpi vector<pii>
#define vvpi vector<vpi>
#define endl '\n'
const int mod = 1e9 + 7;
using namespace std;
const int N = 2e5+5;
const int inf = 1e12;
void solve() {
int n, m;
cin >> n >> m;
string grid[n];
F(i, 0, n) cin >> grid[i];
vvi dist(n, vi(m, inf));
deque<pii> q;
q.push_back({0, 0});
dist[0][0] = 1;
while(q.size()) {
pii cur = q.front();
q.pop_front();
int dy[] = {1, 0, -1, 0};
int dx[] = {0, 1, 0, -1};
F(i, 0, 4) {
int ny = cur.fi + dy[i];
int nx = cur.se + dx[i];
if(ny < 0 || nx < 0 || ny >= n || nx >= m || dist[ny][nx] != inf || grid[ny][nx] == '.') continue;
if(grid[cur.fi][cur.se] == grid[ny][nx]) {
dist[ny][nx] = dist[cur.fi][cur.se];
q.push_front({ny, nx});
} else {
dist[ny][nx] = dist[cur.fi][cur.se] + 1;
q.push_back({ny, nx});
}
}
}
int ans = 1;
F(i, 0, n) {
F(j, 0, m) {
//cout << (dist[i][j] == inf ? "." : to_string(dist[i][j]));
if(dist[i][j] != inf) ans = max(ans, dist[i][j]);
}
//cout << endl;
}
cout << ans << endl;
}
int32_t main() {
cin.tie(0); ios_base::sync_with_stdio(0);
#ifdef Local
freopen("local.in", "r", stdin);
freopen("local.out", "w", stdout);
#endif
int t = 1;
//cin >> t;
while(t--) solve();
}
