#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> pii;
#define ff first
#define ss second
#define MP make_pair
const int mxn = 4040;
int dis[mxn][mxn], n, m;
bool vis[mxn][mxn];
char c[mxn][mxn];
int di[] = {1, -1, 0, 0};
int dj[] = {0, 0, -1, 1};
void bfs(int si, int sj) {
dis[si][sj] = 1;
priority_queue<pair<int, pii>> pq;
pq.push(MP(-1, MP(si, sj)));
while(pq.size()) {
int d = -pq.top().ff;
int i = pq.top().ss.ff;
int j = pq.top().ss.ss;
pq.pop();
if(c[i][j] == '.') continue;
if(dis[i][j] != d) continue;
if(vis[i][j]) continue;
vis[i][j] = 1;
// cout << i << ' ' << j << ": " << d << ' ' << dis[i][j] << endl;
for(int x = 0; x < 4; x++) {
int I = i + di[x];
int J = j + dj[x];
if(c[I][J] == '.') continue;
if(c[i][j] == c[I][J]) {
dis[I][J] = min(dis[I][J], d);
// cout << i << ' ' << j << " -> " << I << ' ' << J << " = " << d << endl;
pq.push(MP(-d, MP(I, J)));
}
else {
dis[I][J] = min(dis[I][J], d + 1);
// cout << i << ' ' << j << " -> " << I << ' ' << J << " - " << d + 1 << endl;
pq.push(MP(-d-1, MP(I, J)));
}
}
}
}
int main() {
cin >> n >> m;
for(int i = 1; i <= n; i++) {
for(int j = 1; j <= m; j++) {
cin >> c[i][j];
}
}
for(int i = 1; i <= n; i++)
c[i][0] = c[i][m + 1] = '.';
for(int j = 1; j <= m; j++)
c[0][j] = c[n + 1][j] = '.';
memset(dis, 0x3f, sizeof dis);
bfs(1, 1);
int ans = 0;
for(int i = 1; i <= n; i++) {
for(int j = 1; j <= m; j++) {
int d = dis[i][j];
if(c[i][j] == '.') d = 0;
// printf("%3d", d);
ans = max(ans, d);
}
// cout << endl;
}
cout << ans << endl;
return 0;
}
