#include<bits/stdc++.h>
using namespace std;
typedef pair<int,int> pii;
#define ff first
#define sc second
int const INF = 2e9;
vector<int> di = {1, -1, 0, 0}, dj = {0, 0, 1, -1};
int main(){
// freopen("A.IN", "r", stdin);
// freopen("A.OUT", "w", stdout);
ios_base::sync_with_stdio(0);
cin.tie(nullptr);
int n, m; cin >> n >> m;
vector<string> grid(n);
for(auto &it : grid) cin >> it;
vector<vector<int>> min_d(n, vector<int> (m, INF));
min_d[0][0] = 1;
deque<pii> q;
q.push_back({0,0});
int ans = 0;
while(!q.empty()){
pii cur = q.front();
q.pop_front();
ans = max(ans, min_d[cur.ff][cur.sc]);
for(int i = 0; i < n; i++){
int ni = cur.ff + di[i];
int nj = cur.sc + dj[i];
if(ni < 0 || ni >= n || nj < 0 || nj >= m) continue;
if(min_d[ni][nj] != INF || grid[ni][nj] == '.') continue;
if(grid[cur.ff][cur.sc] == grid[ni][nj]){
min_d[ni][nj] = min_d[cur.ff][cur.sc];
q.push_front({ni, nj});
}
else {
min_d[ni][nj] = min_d[cur.ff][cur.sc] + 1;
q.push_back({ni, nj});
}
}
}
cout << ans;
}
