#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define ll long long
#define mid l+(r-l)/2
#define ya cout<<"YES"<<endl;
#define na cout<<"NO"<<endl;
#define all(x) (x).begin(), (x).end()
#define F first
#define S second
#define sz(x) (int)x.size()
#define pb push_back
#define pp pop_back();
//rotate(vec.begin(), vec.begin() + k, vec.end());
//set<int> S(all(a));
/*if (S.count(key)) {
// ...
}*/
/*if (binary_search(all(vec), key)) {
// ...
}*/
//int pos = partition_point(all(vec), p) - vec.begin();
//Print a binary representation of a number cout << bitset<20>(n) << "\n";
int nxt() {
int x;
cin >> x;
return x;
}
long long lcm(long long x,long long y)
{
return (x*y)/__gcd(x,y);
}
int M=1000000007;
ll fp(ll x,ll y)
{
if(y==0)
return 1;
ll m=fp(x,y/2);
m*=m;
m%=M;
if(y%2==1)
m*=x;
m%=M;
return m;
}
int dx[4]{1, -1, 0, 0},dy[4]{0, 0, 1, -1};
char a[4005][4005];
int depth[4005][4005];
int ans=0;
int n,m;
void bfs(int i,int j)
{
deque<pair<int,int>>q;
depth[i][j]=1;
q.push_back({i,j});
while(!q.empty())
{
int x=q.front().F,y=q.front().S;
q.pop_front();
ans=max(ans,depth[x][y]);
for(int g=0;g<4;g++)
{
int l=x+dx[g],r=y+dy[g];
if(l>=n||l<0||r>=m||r<0)
continue;
if(a[l][r]=='.')
continue;
if(!depth[l][r])
{
int f=0;
if(a[l][r]!=a[x][y])
f=1;
depth[l][r]=depth[x][y]+f;
if(f)
q.push_back({l,r});
else
q.push_front({l,r});
}
}
}
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin>>n>>m;
for(int i=0;i<n;i++)
{
string s;
cin>>s;
for(int j=0;j<m;j++)
a[i][j]=s[j];
}
bfs(0,0);
cout<<ans;
return 0;
}
