#include <bits/stdc++.h>
using namespace std;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int h, w;
cin >> h >> w;
vector<string> s (h);
for (int i = 0; i < h; i++) {
cin >> s[i];
}
deque<pair<pair<short, short>, int>> q;
vector<vector<bool>> odw (h, vector<bool>(w, 0));
q.push_back({{0, 0}, 1});
int maxd = 0;
while (!q.empty()) {
auto x = q.front();
short i = x.first.first, j = x.first.second;
q.pop_front();
if (odw[i][j]) {
continue;
}
maxd = max(maxd, x.second);
odw[i][j] = 1;
if (i != 0 && !odw[i-1][j] && s[i-1][j] != '.') {
if (s[i][j] == s[i-1][j]) {
q.push_front({{i-1, j}, x.second});
}
else {
q.push_back({{i-1, j}, x.second+1});
}
}
if (j != 0 && !odw[i][j-1] && s[i][j-1] != '.') {
if (s[i][j] == s[i][j-1]) {
q.push_front({{i, j-1}, x.second});
}
else {
q.push_back({{i, j-1}, x.second+1});
}
}
if (i != h-1 && !odw[i+1][j] && s[i+1][j] != '.') {
if (s[i][j] == s[i+1][j]) {
q.push_front({{i+1, j}, x.second});
}
else {
q.push_back({{i+1, j}, x.second+1});
}
}
if (j != w-1 && !odw[i][j+1] && s[i][j+1] != '.') {
if (s[i][j] == s[i][j+1]) {
q.push_front({{i, j+1}, x.second});
}
else {
q.push_back({{i, j+1}, x.second+1});
}
}
}
cout << maxd << '\n';
}
