/*
* Author: bubu2006
**/
#include <bits/stdc++.h>
using namespace std;
int main() {
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int H, W;
cin >> H >> W;
vector<string> m(H);
for(int i = 0; i < H; i++) cin >> m[i];
vector<int> dy = {0, 0, -1, 1};
vector<int> dx = {1, -1, 0, 0};
const int INF = 1e8;
vector<vector<int>> d(H, vector<int>(W, INF));
deque<pair<int, int>> q;
q.push_back({0, 0});
d[0][0] = 1;
int ans = 1;
while(!q.empty()) {
pair<int, int> cur = q.front();
int y = cur.first;
int x = cur.second;
ans = max(ans, d[y][x]);
q.pop_front();
for(int k = 0; k < 4; k++) {
int ny = y + dy[k];
int nx = x + dx[k];
if(ny < 0 || ny >= H || nx < 0 || nx >= W) continue;
if(m[ny][nx] == '.') continue;
int w = (m[y][x] != m[ny][nx]);
if(d[ny][nx] > d[y][x] + w) {
d[ny][nx] = d[y][x] + w;
if(w) q.push_back({ny, nx});
else q.push_front({ny, nx});
}
}
}
cout << ans << '\n';
}
// ........ RRR..... FFR.....
// ........ ..RRR... .FRRR...
// ........ ..R..... .FFFFF..
// ........ ..RRRR.R ..RRRFFR
// ........ .....RRR .....FFF
// i had a greedy that always would work but the 0/1 bfs is just too clean
