#include <bits/stdc++.h>
using namespace std;
#define MX 4001
typedef long long LL;
typedef pair<int, int> PR;
typedef tuple<int, int, int> TP;
const int MOD = (int)1e9 + 7;
const int INF = (int)1e9 + 5;
const LL MAXV = (LL)1e18;
using vi = vector<int>;
using vii = vector<vi>;
int H, W;
string md[MX]; //snow meadow
/*
use Disjoint Sets to solve the problem.
(1) Use BFS to find all CCs (each with the same footprint letter R or F) and assign each CC with
an integer ID starting from 0.
(2) Perform a scan on the meadow to discover connectitvity between adjcent CCs with different letters
(3) A bipartite graph or tree, then BFS to find the height of the tree which is the answer.
*/
vector<set<int>> adj;
int solve() {
cin >> H >> W;
//read the snow meadow info
for (int i = 0; i < H; i++)
cin >> md[i];
if (md[0][0] == '.')
return 0;
vector<vector<int>> id(H, vector<int>(W, -1));
int t = 0;
for (int i = 0; i < H; i++)
for (int j = 0; j < W; j++) {
if (md[i][j] == '.' || id[i][j] != -1)
continue;
queue<PR> Q;
Q.push({i, j});
id[i][j] = t;
//BFS to find the CC
while (!Q.empty()) {
int r = Q.front().first, c = Q.front().second;
Q.pop();
int dr = 0, dc = 1;
for (int k = 0; k < 4; k++) {
int nr = r + dr, nc = c + dc;
if (nr >= 0 && nr < H && nc >= 0 && nc < W &&
md[nr][nc] == md[i][j] && id[nr][nc] == -1) {
id[nr][nc] = t;
Q.push({nr, nc});
}
swap(dr, dc);
dc = -dc;
}
}
t++;//next CC
}
adj.resize(t);
//scan adjacency between CCs, to build the bipartite graph
for (int i = 0; i < H; i++)
for (int j = 0; j < W; j++) {
if (id[i][j] == -1)
continue;
int dr = 0, dc = 1;
for (int k = 0; k < 4; k++) {
int r = i + dr, c = j + dc;
if (r >= 0 && r < H && c >= 0 && c < W && id[r][c] != -1 && id[r][c] != id[i][j] && md[r][c] != md[i][j]) {
adj[id[i][j]].insert(id[r][c]);
adj[id[r][c]].insert(id[i][j]);
}
swap(dr, dc);
dc = -dc;
}
}
vector<int> d(t, -1);
queue<int> Q2;
Q2.push(0); //the root
d[0] = 1;
while (!Q2.empty()) {
int u = Q2.front();
Q2.pop();
for (auto v : adj[u])
if (d[v] == -1) {
d[v] = d[u]+1;
Q2.push(v);
}
}
return *max_element(d.begin(), d.end());
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin.exceptions(cin.failbit);
cout << solve() << endl;
return 0;
}
