#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i = (a); i < (b); i++)
typedef long long ll;
int H, W;
vector<string> grid;
vector<vector<ll>> visited; // bitset ?
priority_queue<vector<ll>> q;
void dfs(int hat, int wat, ll num)
{
visited[hat][wat] = num;
char ch = grid[hat][wat];
if (hat + 1 < H) {
if (visited[hat + 1][wat] == -1 && grid[hat + 1][wat] != '.') {
if (grid[hat + 1][wat] == ch) q.push({-num, hat + 1, wat});
else q.push({-(num + 1), hat + 1, wat});
}
}
if (wat + 1 < W) {
if (visited[hat][wat + 1] == -1 && grid[hat][wat + 1] != '.') {
if (grid[hat][wat + 1] == ch) q.push({-num, hat, wat + 1});
else q.push({-(num + 1), hat, wat + 1});
}
}
if (hat - 1 >= 0) {
if (visited[hat - 1][wat] == -1 && grid[hat - 1][wat] != '.') {
if (grid[hat - 1][wat] == ch) q.push({-num, hat - 1, wat});
else q.push({-(num + 1), hat - 1, wat});
}
}
if (wat - 1 >= 0) {
if (visited[hat][wat - 1] == -1 && grid[hat][wat - 1] != '.') {
if (grid[hat][wat - 1] == ch) q.push({-num, hat, wat - 1});
else q.push({-(num + 1), hat, wat - 1});
}
}
}
int32_t main()
{
cin>>H>>W;
grid.assign(H, "");
rep(i,0,H){
cin>>grid[i];
}
visited.assign(H, vector<ll>(W, -1));
q.push({-1,0,0});
while(!q.empty())
{
vector<ll> x = q.top();
q.pop();
dfs(x[1], x[2], -(x[0]));
}
ll ans = 1;
rep(i,0,H){
rep(j,0,W){
ans = max(ans, visited[i][j]);
}
}
cout << ans;
}
