#include <bits/stdc++.h>
using namespace std;
#define forw(i,a,b) for(ll i=a;i<=b;i++)
#define forb(i,a,b) for(ll i=a;i>=b;i--)
#define fi first
#define se second
#define pb push_back
#define pu push
#define all(a) a.begin(),a.end()
#define getbit(mask,i) ((mask>>(i))&1)
#define minimize(a,b) (a)=min((a),(b))
typedef long long int ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
const ll maxN=5000+5;
const ll mod=1e9+7;
const ll oo=1e18;
const int tx[4]={0,1,0,-1};
const int ty[4]={1,0,-1,0};
char a[maxN][maxN];
int n,m,ans,vis[maxN][maxN];
bool outmap(int x, int y)
{
if (1<=x && x<=n)
if (1<=y && y<=m) return 0;
return 1;
}
void solve()
{
cin>>n>>m;
forw(i,1,n)
forw(j,1,m) cin>>a[i][j];
deque<pii> p;
vis[1][1]=1;
ans=1;
p.push_front({1,1});
while (p.size())
{
int x=p.front().fi;
int y=p.front().se;
p.pop_front();
forw(i,0,3)
{
int xx=x+tx[i];
int yy=y+ty[i];
if (a[xx][yy]!='.' && !vis[xx][yy] && !outmap(xx,yy))
if (a[x][y]==a[xx][yy])
{
vis[xx][yy]=vis[x][y];
p.push_front({xx,yy});
}
else
{
vis[xx][yy]=vis[x][y]+1;
ans=max(ans,vis[xx][yy]);
p.push_back({xx,yy});
}
}
}
cout<<ans;
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
//freopen("bruh.inp","r",stdin);
//freopen("bruh.out","w",stdout);
solve();
return 0;
}
