#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 + 13;
ll t1, n, m, d[N][N], ans, x, y;
ll dx[4] = {0, 0, 1, -1}, dy[4] = {1, -1, 0, 0};
string t;
char s[N][N];
deque <pii> q;
bool st1[N][N], st2[N][N];
pii v;
void solve(){
cin >> n >> m;
forn (i, 1, max (n, m)){
s[i][0] = s[0][i] = s[n + 1][i] = s[i][m + 1] = '.';
}
forn (i, 1, n){
cin >> t;
forn (j, 1, m){
s[i][j] = t[j - 1];
}
}
q.push_back ({1, 1});
d[1][1] = ans = 1;
while (sz(q)){
// for (pii p: q) cout << p.F << " " << p.S << " ";
// cout << endl;
v = q[0];
q.pop_front();
forn (i, 0, 3){
x = v.F + dx[i];
y = v.S + dy[i];
if (s[x][y] != '.' && !d[x][y]){
if (s[x][y] == s[v.F][v.S]){
d[x][y] = d[v.F][v.S];
q.push_front ({x, y});
}
else{
d[x][y] = d[v.F][v.S] + 1;
q.push_back ({x, y});
ans = max (ans, d[x][y]);
}
}
}
}
// 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
*/
