#include <iostream>
#include <deque>
#define NMAX 4000
using namespace std;
int n, m, viz[NMAX+10][NMAX+10], cost[NMAX+10][NMAX+10], ans;
char v[NMAX+10][NMAX+10];
int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, 1, 0, -1};
deque <pair <int, int> > dq;
void bfs()
{ viz[1][1] = 1;
while(!dq.empty())
{ pair <int, int> a = dq.front();
dq.pop_front();
for(int t=0; t<4; t++)
{ pair <int, int> vec = {dx[t] + a.first, dy[t] + a.second};
if(vec.first && vec.first <= n && vec.second && vec.second <= m
&& !viz[vec.first][vec.second])
{ viz[vec.first][vec.second] = 1;
if(v[a.first][a.second] == v[vec.first][vec.second])
{ dq.push_front(vec);
cost[vec.first][vec.second] = cost[a.first][a.second];
}
else
{ dq.push_back(vec);
cost[vec.first][vec.second] = cost[a.first][a.second] + 1;
}
}
}
}
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
cin >> n >> m;
for(int i=1; i<=n; i++)
{ string s;
cin >> s;
for(int j=0; j<m; j++)
{ v[i][j+1] = s[j];
if(s[j] == '.') viz[i][j+1] = 1;
}
}
dq.push_front({1, 1});
bfs();
for(int i=1; i<=n; i++)
for(int j=1; j<=m; j++)
ans = max(ans, cost[i][j]);
cout << ans + 1<< '\n';
return 0;
}
