#include <bits/stdc++.h>
using namespace std;
int dr[]={+1, 0, -1, 0};
int dc[]={0, +1, 0, -1};
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
int n, m;
cin >> n >> m;
char tracks[n][m];
for (int i=0;i<n;i++)
for (int j=0;j<m;j++)
cin >> tracks[i][j];
deque<pair<int,int> > q;
q.push_back({0,0});
int vis[n][m], rez=1;
memset(vis, 0, sizeof(vis));
vis[0][0]=1;
while (!q.empty()) {
int r=q.front().first, c=q.front().second;
q.pop_front();
rez=max(rez, vis[r][c]);
for (int i=0;i<4;i++) {
int nr=r+dr[i], nc=c+dc[i];
if (nr>=0&&nc>=0&&nr<n&&nc<m&&tracks[nr][nc]!='.'&&!vis[nr][nc]) {
if (tracks[nr][nc]!=tracks[r][c]) {
vis[nr][nc]=vis[r][c]+1;
q.push_back({nr, nc});
}
else {
vis[nr][nc]=vis[r][c];
q.push_front({nr, nc});
}
}
}
}
cout << rez;
return 0;
}
