#include <bits/stdc++.h>
using namespace std;
const int INF = 1000000000;
vector<array<int, 2>> del = {{-1, 0}, {1, 0}, {0, 1}, {0, -1}};
bool check(int x, int y, int r, int c){
return x >= 0 && x < r && y >= 0 && y < c;
}
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int h, w;
cin >> h >> w;
char mat[h][w];
for(int i = 0; i < h; i++)
for(int j = 0; j < w; j++)
cin >> mat[i][j];
deque<array<int, 2>> q;
q.push_back({0, 0});
int d[h][w];
for(int i = 0; i < h; i++)
for(int j = 0; j < w; j++)
d[i][j] = INF;
d[0][0] = 1;
while(!q.empty()){
array<int, 2> cur = q.front();
q.pop_front();
int x = cur[0], y = cur[1];
for(auto &[dx, dy] : del){
if(!check(x+dx, y+dy, h, w))
continue;
if(mat[x+dx][y+dy] == '.')
continue;
int nxt = d[x][y] + (mat[x+dx][y+dy] == mat[x][y] ? 0 : 1);
if(d[x+dx][y+dy] <= nxt)
continue;
if(mat[x+dx][y+dy] == mat[x][y])
q.push_front({x+dx, y+dy});
else q.push_back({x+dx, y+dy});
d[x+dx][y+dy] = nxt;
}
}
int ans = 0;
for(int i = 0; i < h; i++)
for(int j = 0; j < w; j++){
if(mat[i][j] == '.')
continue;
ans = max(ans, d[i][j]);
}
cout << ans << '\n';
return 0;
}
