#include<bits/stdc++.h>
using namespace std;
#define in insert
#define fastio ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define endl "\n"
#define Endl "\n"
#define ENDL "\n"
#define fi first
#define se second
#define be begin()
#define en end()
#define pb push_back
typedef long long ll;
typedef long double ld;
const int MOD=1e9+7;
const int MAX=2e5+1;/*
ll binpow(ll a, ll b) {
ld res = 1;
while (b > 0) {
if (b & 1)
res = res * a;
a = a * a;
b >>= 1;
}
return res;
}
unsigned long long power(unsigned long long x,
ll y, ll p)
{
unsigned long long res = 1; // Initialize result
x = x % p; // Update x if it is more than or
// equal to p
while (y > 0)
{
// If y is odd, multiply x with result
if (y & 1)
res = (res * x) % p;
// y must be even now
y = y >> 1; // y = y/2
x = (x * x) % p;
}
return res;
}
unsigned long long modInverse(unsigned long long n,
ll p)
{
return power(n, p - 2, p);
}
*/
ll n , m ;
char grid[4005][4005];
ll vis[4006][4006];
ll level[4006][4006];
ll dx[]={0 , 0 , 1 , -1};
ll dy[]={-1 , 1 , 0 , 0};
bool valid(ll x , ll y)
{
return x>=0 && y>=0 && x<n && y<m && grid[x][y] != '.' && !vis[x][y];
}
ll max1=0;
void bfs(ll x ,ll y)
{
deque<pair<ll,ll>>q;
q.push_front({x,y});
for(int i=0;i<n;i++)
{
for(int j=0;j<m;j++)
{
level[i][j]=-1e18;
}
}
level[x][y]=0;
vis[x][y]=1;
while(!q.empty())
{
pair<ll,ll>p = q.front();
q.pop_front();
max1=max(max1 , level[p.fi][p.se]);
for(int i=0;i<4;i++)
{
ll nx = p.fi + dx[i];
ll ny = p.se + dy[i];
if(!valid(nx , ny))continue;
if(grid[nx][ny]==grid[p.fi][p.se])
{
level[nx][ny]=level[p.fi][p.se];
q.push_front({nx,ny});
}
else
{
level[nx][ny]=level[p.fi][p.se]+1;
q.push_back({nx,ny});
}
vis[nx][ny]=1;
}
}
}
int main()
{
fastio
//freopen("lasers.in","r",stdin);
//freopen("lasers.out","w",stdout);
cin>>n>>m;
for(int i=0;i<n;i++)
{
string s;
cin>>s;
for(int j=0;j<s.size();j++)
{
grid[i][j]=s[j];
}
}
bfs(0 , 0);
cout<<max1+1<<endl;
return 0;
}
/*
5 6
0 4 0
0 3 1
0 1 1
0 2 1
1 2 1
3 4 0
*/
