#include<bits/stdc++.h>
using namespace std;
const long long maxn = 4000 + 10, INF = 1e9 + 10;
long long n, m, h, w;
bool vis[maxn];
char meadow[maxn][maxn];
int main() {
cin >> h >> w;
for (int i = 1; i <= h; i++)
for (int j = 1; j <= w; j++)
cin >> meadow[i][j];
long long adj[4]{1, -1, w, -w};
vector<long long> d(maxn * maxn, INF);
d[1] = 0;
deque<int> q;
q.push_back(1);
while (q.size()) {
int v = q.front();
q.pop_front();
for (int a : adj) {
int u = a + v;
int i = (v-1) / w + 1, j = v % w,
x = (u-1) / w + 1, y = u % w;
if (x <= 0 || y <= 0) continue;
if (x > h || y > w) continue;
if (meadow[x][y] == '.') continue;
int w = !(meadow[i][j] == meadow[x][y]);
if (d[v] + w < d[u]) {
d[u] = d[v] + w;
if (w == 1)
q.push_back(u);
else
q.push_front(u);
}
}
}
long long mx = 0;
for (int i = 1; i <= w * h; i++) {
if (d[i] < INF)
mx = max(mx, d[i]);
}
cout << mx + 1 << '\n';
return 0;
}
