#include <bits/stdc++.h>
using namespace std;
void fastIO() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
}
const int NMAX = 4e3 + 3;
const int di[] = {-1, 0, 1, 0}, dj[] = {0, 1, 0, -1};
int N, M, dp[NMAX][NMAX];
char a[NMAX][NMAX];
bool inside(int lin, int col) {
return lin > 0 && col > 0 && lin <= N && col <= M;
}
void solve() {
cin >> N >> M;
for (int i = 1; i <= N; ++i)
cin >> (a[i] + 1);
dp[1][1] = 1;
deque<pair<int,int>> dq{make_pair(1, 1)};
int ans = 1;
while (!dq.empty()) {
int i, j;
tie(i, j) = dq.front();
dq.pop_front();
if (dp[i][j] > ans)
ans = dp[i][j];
for (int k = 0; k < 4; ++k) {
int iv = i + di[k], jv = j + dj[k];
if (!inside(iv, jv) || a[iv][jv] == '.')
continue;
int cost = a[i][j] != a[iv][jv];
if (dp[iv][jv] == 0) {
dp[iv][jv] = dp[i][j] + cost;
if (cost)
dq.push_back(make_pair(iv, jv));
else dq.push_front(make_pair(iv, jv));
}
}
}
cout << ans << '\n';
}
int main() {
fastIO();
solve();
return 0;
}
