#include <bits/stdc++.h>
using namespace std;
#define ForUp(i, a, b) for (int i = (a), _b = (b); i <= _b; i++)
#define ForDn(i, a, b) for (int i = (a), _b = (b); i >= _b; i--)
#define all(a) (a).begin(), (a).end()
#define fi first
#define se second
using ll = long long;
const int N = 4000 + 24, INF = 1e9;
const int dx[] = {1, -1, 0, 0};
const int dy[] = {0, 0, 1, -1};
int n, m; char a[N][N];
int f[N][N];
bool inside(int i, int j) {
return (i >= 1 && i <= n && j >= 1 && j <= m);
}
void solve() {
cin >> n >> m;
ForUp (i, 1, n) ForUp (j, 1, m) {
cin >> a[i][j];
}
ForUp (i, 1, n) ForUp (j, 1, m) {
f[i][j] = INF;
}
f[1][1] = 1;
deque<pair<int, int>> q;
q.push_back({1, 1});
while (q.size()) {
auto [u, v] = q.front();
q.pop_front();
ForUp (dir, 0, 3) {
int i = u + dx[dir], j = v + dy[dir];
if (!inside(i, j) || a[i][j] == '.') continue;
int w = (a[u][v] != a[i][j]);
if (f[u][v] + w < f[i][j]) {
f[i][j] = f[u][v] + w;
if (w) {
q.push_back({i, j});
}
else {
q.push_front({i, j});
}
}
}
}
int res = 0;
ForUp (i, 1, n) ForUp (j, 1, m) {
if (a[i][j] != '.') res = max(res, f[i][j]);
}
cout << res << '\n';
}
signed main() {
cin.tie(0) -> sync_with_stdio(0);
int T = 1; // cin >> T;
while (T--) {
solve();
}
}
