#include <bits/stdc++.h>
#define pll pair<long long, long long>
using namespace std;
char a[4005][4005];
long long p[2000005], r[2000005], dp[2000005], pre[2000005], check[4005][4005], check2[2000005];
queue<pll> q;
queue<long long> q2;
pll p2;
vector<long long> v, adj[2000005];
void makeset(long long x)
{
p[x]=x;
}
long long findset(long long x)
{
if (p[x]!=x) {p[x]=findset(p[x]);};
return p[x];
}
void unionsets(long long x, long long y)
{
x=findset(x);
y=findset(y);
if (x!=y)
{
if (r[x]<r[y]) {swap(x, y);};
p[y]=x;
if (r[x]==r[y]) {r[x]++;};
};
}
int main()
{
long long n, m, i, j;
cin >> n >> m;
for (i=1; i<=n; i++)
{
for (j=1; j<=m; j++)
{
cin >> a[i][j];
if (a[i][j]=='.') {continue;};
makeset((i-1)*m+j);
if (i>1 && a[i-1][j]==a[i][j]) {unionsets((i-1)*m+j, (i-2)*m+j);};
if (j>1 && a[i][j-1]==a[i][j]) {unionsets((i-1)*m+j, (i-1)*m+j-1);};
};
};
q.push(make_pair(1, 1));
check[1][1]=1;
check2[findset(1)]=1;
while (!q.empty())
{
p2=q.front();
q.pop();
i=p2.first; j=p2.second;
if (i>1 && a[i-1][j]!='.' && !check[i-1][j])
{
if (a[i-1][j]!=a[i][j] && !check2[findset((i-2)*m+j)]) {adj[findset((i-2)*m+j)].push_back(findset((i-1)*m+j)); check2[findset((i-2)*m+j)]=1;};
q.push(make_pair(i-1, j));
check[i-1][j]=1;
};
if (j>1 && a[i][j-1]!='.' && !check[i][j-1])
{
if (a[i][j-1]!=a[i][j] && !check2[findset((i-1)*m+j-1)]) {adj[findset((i-1)*m+j-1)].push_back(findset((i-1)*m+j)); check2[findset((i-1)*m+j-1)]=1;};
q.push(make_pair(i, j-1));
check[i][j-1]=1;
};
if (i<n && a[i+1][j]!='.' && !check[i+1][j])
{
if (a[i+1][j]!=a[i][j] && !check2[findset(i*m+j)]) {adj[findset(i*m+j)].push_back(findset((i-1)*m+j)); check2[findset(i*m+j)]=1;};
q.push(make_pair(i+1, j));
check[i+1][j]=1;
};
if (j<m && a[i][j+1]!='.' && !check[i][j+1])
{
if (a[i][j+1]!=a[i][j] && !check2[findset((i-1)*m+j+1)]) {adj[findset((i-1)*m+j+1)].push_back(findset((i-1)*m+j)); check2[findset((i-1)*m+j+1)]=1;};
q.push(make_pair(i, j+1));
check[i][j+1]=1;
};
};
for (i=1; i<=n; i++)
{
for (j=1; j<=m; j++)
{
if (a[i][j]=='.') {continue;};
v.push_back(findset((i-1)*m+j));
};
};
sort(v.begin(), v.end());
v.erase(unique(v.begin(), v.end()), v.end());
for (auto x: v)
{
for (auto y: adj[x]) {pre[y]++;};
};
for (auto x: v)
{
if (pre[x]==0) {q2.push(x); dp[x]=1;};
};
while (!q2.empty())
{
i=q2.front();
q2.pop();
for (auto x: adj[i])
{
dp[x]=max(dp[x], dp[i]+1);
pre[x]--;
if (pre[x]==0) {q2.push(x);};
};
};
cout << dp[findset(1)];
}
