#include<bits/stdc++.h>
using namespace std;
const int dx[]{0,1,0,-1};
const int dy[]{1,0,-1,0};
bool in(int x, int y, int n, int m) {
return (x > -1 && x < n && y > -1 && y < m);
}
int main()
{
int n, m;
cin >> n >> m;
char md[n][m];
for(int i=0; i<n; i++)
for(int j=0; j<m; j++)
cin >> md[i][j];
bool vis[n][m]{};
int d[n][m];
d[0][0] = 1;
int ans = 1;
deque<pair<int,int>> q;
q.push_front({0,0});
while(!q.empty()){
int x=q.front().first;
int y=q.front().second;
q.pop_front();
if(vis[x][y]) continue;
vis[x][y] = true;
ans = max(ans, d[x][y]);
for(int i=0; i<4; i++){
if(md[x+dx[i]][y+dy[i]] == md[x][y]
and in(x+dx[i], y+dy[i], n, m)){
d[x+dx[i]][y+dy[i]] = d[x][y];
q.push_front({x+dx[i], y+dy[i]});
}else{
if(md[x+dx[i]][y+dy[i]] == '.') continue;
if(in(x+dx[i], y+dy[i], n, m)){
d[x+dx[i]][y+dy[i]] = d[x][y]+1;
q.push_back({x+dx[i], y+dy[i]});
}
}
}
}
cout << ans << '\n';
}
