#include <vector>
#include <iostream>
#include <cassert>
#include <cmath>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <set>
#include <algorithm>
#include <iomanip>
using namespace std;
vector<vector<bool>> hasVisited;
vector<string> grid;
vector<pair<int, int>> pos = {{0, 1},
{-1, 0},
{0, -1},
{1, 0}};
int main() {
//freopen("milkorder.in", "r", stdin);
//freopen("milkorder.out", "w", stdout);
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int n, m;
cin >> n >> m;
priority_queue<pair<int, pair<int, int>>> q;
grid.resize(n), hasVisited.resize(n);
for (int i = 0; i < n; i++) {
cin >> grid[i];
hasVisited[i].resize(m);
for (int j = 0; j < m; j++) {
hasVisited[i][j] = false;
}
}
q.push({0, {0, 0}});
int myMax = 0;
while (!q.empty()) {
pair<int, int> loc = q.top().second;
int dist = -q.top().first;
myMax = max(myMax, dist);
q.pop();
if (hasVisited[loc.first][loc.second]) {
continue;
}
hasVisited[loc.first][loc.second] = true;
for (auto p: pos) {
int dx = p.first;
int dy = p.second;
pair<int,int> nxt = {p.first + dx, p.second + dy};
if (nxt.first >= 0 && nxt.second >= 0 && nxt.first < n && nxt.second < m
&& grid[nxt.first][nxt.second] != '.') {
if (hasVisited[nxt.first][nxt.second]) {
myMax = max(myMax, dist + (grid[nxt.first][nxt.second] != grid[loc.first][loc.second]));
continue;
}
q.push(make_pair(-dist - (grid[nxt.first][nxt.second] != grid[loc.first][loc.second]),
make_pair(loc.first + dx, loc.second + dy)));
}
}
}
cout << myMax;
}
