#include <bits/stdc++.h>
using namespace std;
const int N = 1005;
const int INF = 1e9;
int r, c;
char a[N][N];
int d[N][N];
int dx[4] = {-1, 1, 0, 0};
int dy[4] = {0, 0, -1, 1};
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> r >> c;
for (int i = 1; i <= r; i++) {
for (int j = 1; j <= c; j++) {
cin >> a[i][j];
d[i][j] = INF;
}
}
deque<pair<int,int>> q;
d[1][1] = 0;
q.push_front({1, 1});
while (!q.empty()) {
int x = q.front().first;
int y = q.front().second;
q.pop_front();
for (int k = 0; k < 4; k++) {
int nx = x + dx[k];
int ny = y + dy[k];
if (nx < 1 || nx > r || ny < 1 || ny > c) continue;
if (a[nx][ny] == '*') continue;
int w = (a[nx][ny] != a[x][y]);
if (d[nx][ny] > d[x][y] + w) {
d[nx][ny] = d[x][y] + w;
if (w == 0) q.push_front({nx, ny});
else q.push_back({nx, ny});
}
}
}
int ans = 0;
for (int i = 1; i <= r; i++) {
for (int j = 1; j <= c; j++) {
if (a[i][j] != '*') ans = max(ans, d[i][j]);
}
}
cout << ans + 1 << '\n';
return 0;
}
