#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define ii pair<int, int>
const int mxN = 5e3;
int dx[4] = {0, 1, 0, -1};
int dy[4] = {1, 0, -1, 0};
int n, m;
string s[mxN];
int ans[mxN][mxN];
bool check(int x, int y) {
return (x >=0 && x < n && y >= 0 && y < m && s[x][y] != '.');
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> m;
for (int i = 0; i < n; ++i) cin >> s[i];
deque<ii> dq;
dq.pb({0, 0});
ans[0][0] = 1;
int kq =0 ;
while(dq.size()) {
ii it = dq.front();
dq.pop_front();
kq = max(kq, ans[it.first][it.second]);
for (int i = 0; i < 4; ++i) {
int x = it.first + dx[i];
int y = it.second + dy[i];
if (check(x, y) && ans[x][y] == 0) {
if (s[x][y] == s[it.first][it.second]) {
ans[x][y] = ans[it.first][it.second];
dq.push_front({x, y});
} else {
ans[x][y] = ans[it.first][it.second] + 1;
dq.push_back({x, y});
}
}
}
}
cout << kq;
return 0;
}
