#include <bits/stdc++.h>
using namespace std;
int directions_x[4]{1,-1,0,0};
int directions_y[4]{0,0,1,-1};
int n,m,depth[4000][4000],ans=1;
string snow[4000];
bool inside(int x,int y) {
return (x>-1 && x<n && y>-1 && y<m && snow[x][y]!='.');
}
int main() {
cin >> n >> m;
for (int i=0; i<n; i++) {
cin >> snow[i];
}
deque<pair<int,int>> q;
q.push_back({0,0});
depth[0][0]=1;
while (q.size()) {
pair<int,int> c=q.front();
q.pop_front();
ans=max(ans,depth[c.first][c.second]);
for (int i=0; i<4; i++) {
int x=c.first+directions_x[i],y=c.second+directions_y[i];
if (inside(x,y) && depth[x][y]==0) {
if (snow[x][y]==snow[c.first][c.second]) {
depth[x][y]=depth[c.first][c.second];
q.push_front({x,y});
} else {
depth[x][y]=depth[c.first][c.second] + 1;
q.push_back({x,y});
}
}
}
}
cout << ans;
}
