#include <bits/stdc++.h>
#define pb push_back
#define er erase
#define in insert
#define s(a, x, y) sort(a.begin()+x, a.begin()+y);
#define r(a, x, y) reverse(a.begin()+x, a.begin()+y);
#define mp make_pair
#define F first
#define S second
#define ll long long
#define ld long double
#define forn(i, a, b) for(int i=a; i<=b; i++)
#define form(i, a, b) for(int i=a; i>=b; i--)
#define PI 3.14159265358979
#define inf 2147483647
#define sp setprecision
#define pii pair <int, int>
#define gcd __gcd
#define endl '\n'
#define sz(a) (int)a.size()
using namespace std;
const ll N = 4000 + 5;
ll t1, n, m, d[N][N], ans;
vector <pii> g[N][N];
string t;
char s[N][N];
deque <pii> q;
bool u[N][N], st1[N][N], st2[N][N];
pii v;
void solve(){
cin >> n >> m;
forn (i, 1, n){
cin >> t;
forn (j, 1, m){
s[i][j] = t[j - 1];
if (i > 1 && s[i][j] != '.' && s[i - 1][j] != '.') {
g[i][j].pb (mp (i - 1, j));
g[i - 1][j].pb (mp (i, j));
if (s[i][j] == s[i - 1][j]) st2[i][j] = 0;
else st2[i][j] = 1;
}
if (j > 1 && s[i][j] != '.' && s[i][j - 1] != '.') {
if (s[i][j] == '.' || s[i][j - 1] == '.') continue;
g[i][j].pb (mp (i, j - 1));
g[i][j - 1].pb (mp (i, j));
if (s[i][j] == s[i][j - 1]) st1[i][j] = 0;
else st1[i][j] = 1;
}
}
}
q.push_back ({1, 1});
d[1][1] = 1;
u[1][1] = 1;
while (q.size()){
v = q[0];
q.pop_front();
for (pii to: g[v.F][v.S]){
if (!u[to.F][to.S]){
u[to.F][to.S] = 1;
d[to.F][to.S] = d[v.F][v.S];
if (v.F == to.F && !st1[v.F][max (v.S, to.S)] || v.S == to.S && !st2[max (v.F, to.F)][v.S]) q.push_front (to);
else {
q.push_back (to);
d[to.F][to.S] ++;
}
ans = max (ans, d[to.F][to.S]);
}
}
}
// forn (i, 1, n){
// forn (j, 1, m){
// cout << d[i][j];
// }
// cout << endl;
// }
cout << ans << endl;
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
// cin >> t1;
t1 = 1;
while (t1 --){
solve();
}
return 0;
}
/*
5
0.50 0.29 0.49 0.95 0.66
2 3
0 3
3 4
2 1
5
0.50 0.29 0.49 0.95 0.83
2 3
0 3
3 4
2 1
1
4 0.66
*/
