#include <bits/stdc++.h>
#define DEBUG 0
using namespace std;
const int N = 4e3 + 10;
const int INF = 1e9 + 7;
const int r[] = {-1, 0, 1, 0};
const int c[] = {0, -1, 0, 1};
char a[N][N];
int dist[N][N];
int main() {
cin.tie(0)->sync_with_stdio(0);
int h, w;
cin >> h >> w;
for(int i = 1; i <= h; i++) {
cin >> (a[i] + 1);
}
int ans = 0;
deque <pair <int, int>> dq;
dq.emplace_back(1, 1);
dist[1][1] = 1;
while(!dq.empty()) {
auto [xi, yi] = dq.front();
dq.pop_front();
ans = max(ans, dist[xi][yi]);
for(int d = 0; d < 4; d++) {
int xj = xi + r[d], yj = yi + c[d];
if(xj < 1 or xj > h or yj < 1 or yj > w or a[xj][yj] == '.') {
continue;
}
int w = (a[xi][yi] != a[xj][yj]);
if(dist[xj][yj] == 0) {
dist[xj][yj] = dist[xi][yi] + w;
if(w == 1) {
dq.emplace_back(xj, yj);
}
else {
dq.emplace_front(xj, yj);
}
}
}
}
cout << ans;
return 0;
}
