#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pll pair<ll,ll>
#define pii pair<int,int>
#define fs first
#define sc second
#define tlll tuple<ll,ll,ll>
#define tiii tuple<int,int,int>
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,popcnt,sse4")
const int mxn = 4040;
int N,M;
string arr[mxn];
int dist[mxn][mxn];
deque<tiii> dq;
pii dir[] = {{0,1},{0,-1},{1,0},{-1,0}};
int main(){
ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
memset(dist,-1,sizeof(dist));
cin>>N>>M;
for(int i = 1;i<=N;i++){
cin>>arr[i];
arr[i] = "."+arr[i]+".";
}
arr[0] = arr[N+1] = string(M+2,'.');
dist[1][1] = 1;
dq.push_back(tiii(1,1,1));
while(!dq.empty()){
auto [r,c,d] = dq.front();
dq.pop_front();
if(dist[r][c] != d)continue;
for(auto &dd:dir){
int nr = r+dd.fs,nc = c+dd.sc;
if(arr[nr][nc] == '.')continue;
int nd = d+(arr[nr][nc] != arr[r][c]);
if(dist[nr][nc] == -1||dist[nr][nc]>nd){
dist[nr][nc] = nd;
if(nd != d)dq.push_back(tiii(nr,nc,dist[nr][nc]));
else dq.push_front(tiii(nr,nc,dist[nr][nc]));
}
}
}
int ans = 0;
for(int i = 1;i<=N;i++){
for(int j = 1;j<=M;j++)ans = max(ans,dist[i][j]);
}
cout<<ans<<'\n';
return 0;
}
