#include <bits/stdc++.h>
using namespace std;
const int MAXN = 4e3 + 10;
char a[MAXN][MAXN];
int dist[MAXN][MAXN], marc[MAXN][MAXN];
int dx[] = {0, 0, 1, -1}, dy[] = {1, -1, 0, 0};
int n, m;
bool check(int i, int j){
return i > 0 && j > 0 && i <= n && j <= m && (a[i][j] != '.');
}
int main(){
cin.tie(0)->sync_with_stdio(0);
cin >> n >> m;
for(int i=1; i<=n; i++){
for(int j=1; j<=m; j++){
cin >> a[i][j];
}
}
int ans = 0;
deque<pair<int, int>> q;
q.push_front({n, m}); dist[n][m] = 1; marc[n][m] = 1;
while(!q.empty()){
auto [i, j] = q.front(); q.pop_front();
ans = max(ans, dist[i][j]);
for(int k=0; k<4; k++){
int ni = i + dx[k], nj = j + dy[k];
if(check(ni, nj) && !marc[ni][nj]){
marc[ni][nj] = 1;
if(a[i][j] == a[ni][nj]){
q.push_front({ni, nj});
dist[ni][nj] = dist[i][j];
} else{
q.push_back({ni, nj});
dist[ni][nj] = dist[i][j] + 1;
}
}
}
}
cout << ans << "\n";
return 0;
}
