#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;
int main() {
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;
//cout << dist << " " << loc.first << " " << loc.second << endl;
myMax = max(myMax, dist);
q.pop();
if (hasVisited[loc.first][loc.second]) {
continue;
}
hasVisited[loc.first][loc.second] = true;
for (int dx = -1; dx <= 1; dx++) {
for (int dy = -1; dy <= 1; dy++) {
if (abs(dx) + abs(dy) == 1 && dx + loc.first >= 0 && dy + loc.second >= 0 && dx + loc.first < n && dy + loc.second < m
&& grid[loc.first + dx][loc.second + dy] != '.') {
int new_dist = -dist - (grid[dx + loc.first][dy + loc.second] != grid[loc.first][loc.second]);
q.push(make_pair(new_dist, make_pair(loc.first + dx, loc.second + dy)));
}
}
}
}
cout << myMax;
}
