#include <bits/stdc++.h>
using namespace std;
int H, W;
int dx[4]{-1, 1, 0, 0}, dy[4]{0, 0, -1, 1};
char grid[4000][4000];
int lvls[4000][4000];
bool good(int r, int c){
if(r<0 || r>=H || c<0 || c>=W || lvls[r][c]!=0 || grid[r][c]=='.') return false;
return true;
}
int main() {
//# of F connected componetntes + 1 or # of R compoentns + 1
cin >> H >> W;
for (int r=0; r<H; r++){
for (int c=0; c<W; c++){
cin >> grid[r][c];
}
}
deque<pair<int, int>> dq;
dq.push_back({0, 0});
lvls[0][0]=1;
int ans = 1;
while(!dq.empty()){
int x, y;
tie(x, y) = dq.front();
dq.pop_front();
ans = max(ans, lvls[x][y]);
for (int i=0; i<4; i++){
int xnew = x+dx[i]; int ynew = y+dy[i];
if(!good(xnew, ynew)) continue;
if(grid[xnew][ynew]==grid[x][y]){
lvls[xnew][ynew]=lvls[x][y];
dq.push_front({xnew, ynew});
}
else{
lvls[xnew][ynew]=1+lvls[x][y];
dq.push_back({xnew, ynew});
}
}
}
cout << ans << endl;
}
