#include <iostream>
#include <string>
#include <deque>
#include <vector>
using namespace std;
using vi = vector<int>;
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int R, C;
cin >> R >> C;
char S[R*C];
for(int i = 0; i < R*C; i++) cin >> S[i];
int res = 1;
vi dist(R*C, R*C*5);
dist[0] = 0;
deque<int> tbv;
tbv.push_back(0);
while(!tbv.empty())
{
int u = tbv.front();
tbv.pop_front();
res = max(res, dist[u] + 1);
vi edge;
if(u % C != 0) edge.push_back(u-1);
if(u % C != C-1) edge.push_back(u+1);
if(u / C != 0) edge.push_back(u-C);
if(u / C != R-1) edge.push_back(u+C);
for(int v : edge)
{
int d = (S[u] != S[v]);
if(S[v] == '*') continue;
if(dist[v] <= dist[u] + d) continue;
dist[v] = dist[u] + d;
if(d == 0) tbv.push_front(v);
else tbv.push_back(v);
}
}
cout << res << '\n';
}
