#include <bits/stdc++.h>
#define fi first
#define se second
#define pb push_back
using namespace std;
typedef long long ll;
typedef double dbl;
typedef pair<ll,ll> pii;
typedef pair<ll,pii> piii;
const int maxn = 4e3+5;
ll H,W,A[maxn][maxn],ans,dy[4] = {1,-1,0,0},dx[4] = {0,0,1,-1};
bool vis[maxn][maxn];
string S[maxn];
bool valid(int y, int x){
return y > 0 && x > 0 && y <= H && x <= W && S[y][x] != '.' && !vis[y][x];
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> H >> W;
for(int i =1; i <= H; i++){
cin >> S[i];
S[i] = " "+S[i];
}
if(S[1][1] == '.'){
cout << 0 << '\n';
return 0;
}
vis[1][1] = 1;
priority_queue<piii,vector<piii>,greater<piii>> pq;
pq.push({1,{1,1}});
while(!pq.empty()){
auto cur = pq.top();
pq.pop();
int y = cur.se.fi, x = cur.se.se;;
ans = max(ans,cur.fi);
//cout << cur.fi << " " << y << " " << x << '\n';
A[y][x] = cur.fi;
for(int i =0; i < 4; i++){
int ny = y + dy[i],nx = x+dx[i];
if(!valid(ny,nx))continue;
pq.push({cur.fi + (S[y][x] == S[ny][nx] ? 0:1),{ny,nx}});
vis[ny][nx] = 1;
}
}
cout << ans << '\n';
}
