// problem url: https://oj.uz/problem/view/BOI13_tracks
#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
typedef vector<int> vi;
typedef vector< vector<int> > vii;
typedef pair<int,int> pii;
const int INF = 1e9+7;
int dx[4] = {1,-1,0,0};
int dy[4] = {0,0,1,-1};
int h, w;
vector<string> snow;
bool inside(int x, int y) {
return 0 <= x && x < h && 0 <= y && y < w && snow[x][y] != '.';
}
void solve() {
cin >> h >> w; snow.resize(h);
for (int i = 0; i < h; i++) cin >> snow[i];
if (snow[0][0] == '.') {
cout << 0 << '\n';
return;
}
int ans = 1;
vii d(h, vi(w, INF));
d[0][0] = 1;
deque<pii> dq;
dq.push_back(pii(0,0));
while (!dq.empty()) {
pii u = dq.front(); dq.pop_front();
int ux = u.fi, uy = u.se;
ans = max(ans, d[ux][uy]);
for (int i = 0; i < 4; i++) {
int vx = ux + dx[i], vy = uy + dy[i];
if (!inside(vx, vy)) continue;
int w = (snow[ux][uy] != snow[vx][vy]);
if (d[vx][vy] == INF) {
d[vx][vy] = d[ux][uy] + w;
if (w) dq.push_back(pii(vx,vy));
else dq.push_front(pii(vx,vy));
}
}
}
cout << ans << '\n';
}
int main() {
ios::sync_with_stdio(0); cin.tie(0);
int tt = 1;
// cin >> tt;
while (tt--) solve();
return 0;
}
