#include<bits/stdc++.h>
using namespace std;
const int MAX_N = 4005;
int dis[MAX_N][MAX_N],n,m,u,v,x,y,w,ans;
int dx[4] = {1,0,-1,0};
int dy[4] = {0,1,0,-1};
char c[MAX_N][MAX_N];
string s;
deque<pair<int,int> > q;
int main()
{
cin >> n >> m;
for(int i = 1;i <= n;i++)
{
cin >> s;
for(int j = 1;j <= n;j++)
c[i][j] = s[j-1],dis[i][j] = 2*MAX_N;
}
dis[1][1] = 1;
q.push_back({1,1});
while(!q.empty())
{
tie(u,v) = q.front();
q.pop_front();
for(int i = 0;i < 4;i++)
{
x = u+dx[i],y = v+dy[i];
if(x < 1||x > n||y < 1||y > n||c[x][y] == '.') continue;
if(c[u][v] == c[x][y]) w = 0;
else w = 1;
if(dis[x][y] > dis[u][v]+w)
{
dis[x][y] = dis[u][v]+w;
if(w == 1) q.push_back({x,y});
else q.push_front({x,y});
}
}
}
for(int i = 1;i <= n;i++)
for(int j = 1;j <= m;j++)
if(c[i][j] != '.')
ans = max(ans,dis[i][j]);
cout << ans << '\n';
return 0;
}
