#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#define pii pair<int, int>
using namespace std;
const int sz = 4005;
int n, m;
string a[sz];
int d[sz][sz];
int dx[] = {0, -1, 1, 0};
int dy[] = {1, 0, 0, -1};
bool check(int x, int y) {
return x >= 0 && x < n && y >= 0 && y < m && a[x][y] != '.';
}
int bfs() {
for (int i = 0; i < n; ++i)
fill(d[i], d[i] + m, -1);
deque<pii> q;
d[0][0] = 1;
q.push_front({0, 0});
int res = 1;
while (!q.empty()) {
auto [x, y] = q.front(); q.pop_front();
for (int i = 0; i < 4; ++i) {
int nx = x + dx[i], ny = y + dy[i];
if (!check(nx, ny)) continue;
if (d[nx][ny] == -1) {
if (a[nx][ny] == a[x][y]) {
d[nx][ny] = d[x][y];
q.push_front({nx, ny});
} else {
d[nx][ny] = d[x][y] + 1;
q.push_back({nx, ny});
}
res = max(res, d[nx][ny]);
}
}
}
return res;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> m;
for (int i = 0; i < n; ++i)
cin >> a[i];
cout << bfs() << '\n';
return 0;
}
