#include <iostream>
#include <deque>
using namespace std;
const int N = 5000;
char a[N][N];
int Min[N][N];
deque<pair<int,int>> vc = {{0, -1}, {0, 1}, {-1, 0}, {1, 0}};
int main(){
int n, m, Mx = 1;
cin>>n>>m;
for (int i=1;i<=n;i++){
for (int j=1;j<=m;j++)
cin>>a[i][j];
}
for (int i=0;i<=n+1;i++){
for (int j=0;j<=m+1;j++)
Min[i][j] = 1e9;
}
Min[1][1] = 1;
deque<pair<int,int>> Q;
Q.push_back({1, 1});
while (Q.size() > 0){
auto [i, j] = Q.front();
Q.pop_front();
for (auto [ia, ja] : vc){
int I = i + ia, J = j + ja;
int c = (a[i][j] != a[I][J]);
if (min(I, J) < 1 or I > n or J > m or a[I][J] == '.' or Min[I][J] <= Min[i][j] + c)
continue;
Min[I][J] = Min[i][j] + c;
if (c == 1)
Q.push_back({I, J});
else
Q.push_front({I, J});
// if (Min[I][J] == 3)
// cout<<I<<" "<<J<<endl;
Mx = max(Mx, Min[I][J]);
}
}
cout<<Mx<<'\n';
// for (int i=1;i<=n;i++){
// for (int j=1;j<=m;j++)
// cout<<(a[i][j] == '.' ? 0 : Min[i][j]);
// cout<<'\n';
// }
}
