// https://oj.uz/problem/view/BOI13_tracks
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using dbl = long double;
using ll = long long;
using str = string;
using ch = char;
using vll = vector<ll>;
using vdbl = vector<dbl>;
using vvll = vector<vll>;
using pll = pair<ll, ll>;
using mpll = map<ll, ll>;
using vpll = vector<pll>;
#define eb emplace_back
#define pb push_back
#define fo(i, k, n) \
for (ll i = k; k < n ? i < n : i > n; k < n ? i += 1 : i -= 1)
#define fu(i, k, n) for (ll i = k; i <= n; i++)
#define fd(i, k, n) for (ll i = k; i >= n; i--)
#define tin0(a, n) fo(i, 0, n) cin >> a[i]
#define tin1(a, n) fu(i, 1, n) cin >> a[i]
#define all(v) v.begin(), v.end()
#define yes cout << "YES" << endl
#define no cout << "NO" << endl
#define f first
#define s second
typedef __gnu_pbds::tree<int, __gnu_pbds::null_type, less<int>,
__gnu_pbds::rb_tree_tag,
__gnu_pbds::tree_order_statistics_node_update>
ordered_set;
ll pow(ll a, ll b) {
ll res = 1;
while (b > 0) {
if (b & 1) res *= a;
a *= a;
b >>= 1;
}
return res;
}
ll modpow(ll a, ll b, ll m) {
ll res = 1;
while (b) {
if (b & 1) res = (res * a) % m;
a = (a * a) % m;
b >>= 1;
}
return res;
}
ll inv(ll a, ll m) { return modpow(a, m - 2, m); }
void solve() {
ll h, w;
cin >> h >> w;
vector<vector<ch>> grid(h, vector<ch>(w));
fu(i, 0, h - 1) {
fu(j, 0, w - 1) { cin >> grid[i][j]; }
}
auto inside = [&](ll x, ll y) {
return x < h && y < w && x > -1 && y > -1 && grid[x][y] != '.';
};
deque<pll> q;
vll dx = {1, -1, 0, 0};
vll dy = {0, 0, 1, -1};
vvll d(h, vll(w, 0));
q.push_front({0, 0});
d[0][0] = 1;
ll ans = 1;
while (!q.empty()) {
pll c = q.front();
q.pop_front();
ans = max(ans, d[c.f][c.s]);
fu(i, 0, 3) {
ll x = c.f + dx[i], y = c.s + dy[i];
if (inside(x, y) && d[x][y] == 0) {
if (grid[x][y] == grid[c.f][c.s]) {
d[x][y] = d[c.f][c.s];
q.push_front({x, y});
} else {
d[x][y] = d[c.f][c.s] + 1;
q.push_back({x, y});
}
}
}
}
cout << ans << endl;
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(0);
// ll t;
// cin >> t;
// while (t--) {
// solve();
// }
solve();
return 0;
}
