#include <bits/stdc++.h>
using namespace std;
char g[4005][4005];
int ans[4005][4005];
int visited[4005][4005];
int dx[] = {0,1,0,-1}, dy[] = {1, 0, -1, 0};
inline int ReadInt() {
int x = 0;
char ch = getchar();
while (ch < '0' || ch > '9') ch = getchar();
while (ch >= '0' && ch <= '9'){
x = (x << 3) + (x << 1) + ch - '0';
ch = getchar();
}
return x;
}
int main(){
ios::sync_with_stdio(0);cin.tie(0);
int h,w,maxi = 0;
cin >> h >> w;
for(int i=1;i<=h;i++){
for(int j=1;j<=w;j++){
cin >> g[i][j];
}
}
for(int i=1;i<=4000;i++)fill(ans[i] , ans[i] + 4005, 2e9 +5);
deque<pair<int, int> >q;
q.push_back(make_pair(1, 1));
ans[1][1] = 0;
while(!q.empty()){
int x = q.front().first;
int y = q.front().second;
q.pop_front();
if(visited[x][y] == true)continue;
visited[x][y] = true;
for(int i=0;i<4;i++){
int x1 = x + dx[i];
int y1 = y + dy[i];
if(x1 < 1 || x1 > h || y1 < 1 ||y1 > w)continue;
if(g[x1][y1] == '.')continue;
int ans1 = 0;
if(g[x1][y1] != g[x][y])ans1++;
ans[x1][y1] = min(ans[x1][y1], ans[x][y] + ans1);
if(ans1 == 0)q.push_front(make_pair(x1, y1));
else q.push_back(make_pair(x1 , y1));
}
}
for(int i=1;i<=h;i++){
for(int j=1;j<=w;j++){
if(g[i][j] == '.')continue;
maxi = max(maxi, ans[i][j]);
}
}
cout << maxi + 1;
}
