#include<bits/stdc++.h> using namespace std; #define int long long #define F first #define S second signed main(){ ios::sync_with_stdio(0);cin.tie(0);cout.tie(0); int n,m;cin >> n >> m; vector<vector<char>> a(n + 1,vector<char> (m + 1)); for(int i = 1;i <= n;i++) for(int j = 1;j <= m;j++) cin >> a[i][j]; auto inside = [&](int i,int j) -> bool{ return i >= 1 && j >= 1 && i <= n && j <= m && a[i][j] != '.'; }; vector<vector<int>> d(n + 1,vector<int> (m + 1)); deque<pair<int,int>> q; q.push_front({1,1}); d[1][1] = 1; const int dx[] = {1,-1,0,0}; const int dy[] = {0,0,-1,1}; int ans = 0; while(!q.empty()){ auto top = q.front(); q.pop_front(); int i = top.F; int j = top.S; ans = max(ans,d[i][j]); for(int t =0 ;t < 4;t++){ int x = i + dx[t]; int y = j + dy[t]; if(inside(x,y) && d[x][y] == 0){ if(a[x][y] == a[i][j]){ d[x][y] = d[i][j]; q.push_front({x,y}); } else{ d[x][y] = d[i][j] + 1; q.push_back({x,y}); } } } } cout << ans << '\n'; }