#include<bits/stdc++.h>
using namespace std;
#define in array<int, 2>
#define pf push_front
#define pb push_back
#define pob pop_back
#define pof pop_front
#define fast() ios_base::sync_with_stdio(false); cin.tie(NULL)
const int LMX = 2e7;
const int INF = LMX+1e5;
char g[LMX]; int n, m;
vector<int> d(LMX, INF);
signed main()
{
fast();
cin >> n >> m;
vector<int> dt = {+m, -m, +1, -1};
for(int i = 0; i < m*n; i++)
cin >> g[i];
deque<int> pq;
pq.pf(0); d[0] = 0;
while(pq.size())
{
int u = pq.front(); pq.pof();
for(auto x: dt)
{
int v = u+x;
if(v < 0 || (v >= (n*m)) || (g[v] == '.'))
continue;
int cn = (g[u] != g[v]);
if(d[v] > (d[u]+cn))
{
d[v] = d[u]+cn;
if(cn)
pq.pb(v);
else
pq.pf(v);
}
}
}
int ans = 0;
for(int i = 0; i < n*m; i++)
{
if(g[i] != '.')
ans = max(ans, ++d[i]);
}
cout << ans << "\n";
return 0;
}
