/*
* Created: 2022-06-05 19:50
*/
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
using namespace chrono;
// using namespace atcoder
template <typename T>
using ordered_set =
tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long ll;
typedef long double ld;
const ll inf = 1e18;
#define pii pair<int,int>
#define pll pair<ll,ll>
#define vi vector<int>
#define vll vector<ll>
#define rep(i, a, b) for(int i = (a);i<(b);i++)
#define repn(i, a, b) for(int i = (a);i>=(b);i--)
#define ss second
#define ff first
#define mkp make_pair
#define pb push_back
#define all(x) (x).begin(), (x).end()
template<typename T>
auto operator<<(ostream &os, T&v)->decltype(v.begin(), os){
os << "[";
int f = 0;
for(auto i:v) {
if(f++)os << ", ";
os << i;
}
os << "]";
return os;
}
template<typename F, typename S>
ostream& operator<<(ostream &os, pair<F, S> const &p) {
return os << "(" << p.first << ", " << p.second << ")";
}
ostream& operator<<(ostream &os, string& s) {
for(char i:s){
os << i;
}
return os;
}
void debug(){}
template<typename T, typename... V>
void debug(T t, V... v) {
cerr << t;
if(sizeof...(v)) {
cerr << ", "; debug(v...);
}
}
#ifdef LOCAL
#define dbg(x...) cerr << "[" << #x << "]: " << "["; debug(x); cerr << "]\n";
#else
#define dbg(x...)
#endif
struct node {
int x, y;
int w;
node() {
w=0,x=0,y=0;
}
};
int ax[] = {0, 0, 1, -1};
int ay[] = {1, -1, 0, 0};
void solve() {
int n, m;cin >> n >> m;
vector<string> v(n);
rep(i,0,n)cin>>v[i];
// ff -> 0, 1
// ss -> x, y
deque<node> dq;
dq.push_back(node());
vector<vector<bool>> vis(n, vector<bool> (m,0));
ll ans = 1;
while(!dq.empty()) {
node at = dq.front();
dq.pop_front();
if(vis[at.x][at.y])continue;
vis[at.x][at.y] = 1;
ans = max(ans, (ll)at.w+1);
for(int i = 0;i<4;i++) {
if(at.x + ax[i] >= 0 && at.x + ax[i] < n && at.y + ay[i] >= 0 && at.y + ay[i] < m) {
if(v[at.x+ax[i]][at.y+ay[i]]=='.')continue;
if(v[at.x+ax[i]][at.y+ay[i]]==v[at.x][at.y]){
node to = node();
to.x=at.x + ax[i];
to.y=at.y+ay[i];
to.w = at.w;
dq.push_front(to);
}
else {
node to = node();
to.x=at.x + ax[i];
to.y=at.y+ay[i];
to.w = at.w+1;
dq.push_back(to);
}
}
}
}
cout << ans << "\n";
}
int main () {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t = 1;
//~ cin >> t;
while(t--) {
solve();
}
return 0;
}
