#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll mx = 4e3;
ll n, m;
vector<string> snow(mx);
bool inside(ll x, ll y)
{
return x >= 0 && x < n && y >= 0 && y < m && snow[x][y] != '.';
}
int main()
{
vector<ll> dx = {-1, 1, 0, 0}, dy = {0, 0, -1, 1};
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> m;
for (ll i = 0; i < n; ++i) {
cin >> snow[i];
}
deque<pair<ll, ll>> que;
que.push_back({0, 0});
ll ans = 1;
vector<vector<ll>> depth(mx, vector<ll>(mx));
depth[0][0] = 1;
while (que.size()) {
auto u = que.front();
ll x = u.first, y = u.second;
que.pop_front();
ans = max(ans, depth[x][y]);
for (ll i = 0; i < 4; ++i) {
if (inside(x + dx[i], y + dy[i]) && !depth[x + dx[i]][y + dy[i]]) {
if (snow[x][y] == snow[x + dx[i]][y + dy[i]]) {
que.push_front({x + dx[i], y + dy[i]});
depth[x + dx[i]][y + dy[i]] = depth[x][y];
}
else {
que.push_back({x + dx[i], y + dy[i]});
depth[x + dx[i]][y + dy[i]] = depth[x][y] + 1;
}
}
}
}
cout << ans;
}
