#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define db double
#define pii pair<int, int>
#define fi first
#define se second
#define pb push_back
#define all(x) begin(x), end(x)
#define allr(x) rbegin(x), rend(x)
#define szx(x) ((int)(x).size())
#define FOR(i, a, b) for (int i = a, _b = (b); i <= _b; ++i)
#define ROF(i, a, b) for (int i = a, _b = (b); i >= _b; --i)
#define REP(i, n) for (int i = 0, _n = (n); i < _n; ++i)
#define endl '\n'
#define inf 1000000007
#define mod 1000000007
using namespace std;
using namespace __gnu_pbds;
void setIO(string filename = "") {
ios::sync_with_stdio(0);
cin.tie(0);
if (!filename.empty()) {
if (ifstream(filename + ".in")) {
freopen((filename + ".in").c_str(), "r", stdin);
freopen((filename + ".out").c_str(), "w", stdout);
}
}
}
int dx[]{0, 1, -1, 0};
int dy[]{1, 0, 0, -1};
int h, w;
vector<vector<char>> table;
bool valid(int x, int y) { return (x >= 0 && y >= 0 && x < h && y < w && table[x][y] != '.'); }
void solve() {
cin >> h >> w;
table.assign(h, vector<char>(w));
REP(i, h) REP(j, w) cin >> table[i][j];
int ans = 0;
vector<vector<int>> dis(h, vector<int>(w, 1e9));
deque<pii> dq;
dq.pb({0, 0});
dis[0][0] = 1;
while (!dq.empty()) {
pii v = dq.front();
dq.pop_front();
ans = max(ans, dis[v.fi][v.se]);
#define d(x) (x).fi][(x).se
REP(i, 4) {
if (valid(v.fi + dx[i], v.se + dy[i]) && dis[v.fi + dx[i]][v.se + dy[i]] == 1e9) {
if (table[d(v)] == table[v.fi + dx[i]][v.se + dy[i]]) {
dis[v.fi + dx[i]][v.se + dy[i]] = dis[d(v)];
dq.push_front({v.fi + dx[i], v.se + dy[i]});
} else {
dis[v.fi + dx[i]][v.se + dy[i]] = dis[d(v)] + 1;
dq.push_back({v.fi + dx[i], v.se + dy[i]});
}
}
}
}
cout << ans;
}
void preprocess() {}
int main() {
setIO("main");
int t = 1;
// cin >> t;
preprocess();
while (t--) { solve(); }
}
