#include<bits/stdc++.h>
#define MAX 4010
using namespace std;
struct state {
int y, x, d;
state(int y, int x, int d) {
this->y = y;
this->x = x;
this->d = d;
}
};
int n, m, s;
char mat[MAX][MAX];
bool visited[MAX][MAX];
deque<state> dq;
int dy[] = {1, 0, -1, 0};
int dx[] = {0, 1, 0, -1};
bool valid(int y, int x) {
return y>=1 && y<=n && x>=1 && x<=m && !visited[y][x] && mat[y][x]!='.';
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> m;
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++)
cin >> mat[i][j];
dq.push_front(state(1,1,1));
while(!dq.empty()) {
state st = dq.front();
dq.pop_front();
visited[st.y][st.x] = true;
s = max(s, st.d);
for(int i=0;i<4;i++) {
int nx = st.x+dx[i];
int ny = st.y+dy[i];
if(!valid(ny,nx)) continue;
if(mat[st.y][st.x]==mat[ny][nx])
dq.push_front(state(ny,nx,st.d));
else
dq.push_back(state(ny,nx,st.d+1));
}
}
cout << s;
return 0;
}
