#include <bits/stdc++.h>
using namespace std;
#define yes cout<<"YES"<<'\n'
#define no cout<<"NO"<<'\n'
#define si size()
#define fi first
#define se second
#define ll long long
#define sr sort
#define pb push_back
const ll MAXN=4e3+5,INF=1e9,MOD=1e9+7;
ll n,m,i,j,k,p,dem,t,sum,ans,dist[MAXN][MAXN],b[4]={0,0,1,-1},c[4]={1,-1,0,0},timego;
string s[MAXN];
void dfs(ll stx,ll sty){
deque<pair<ll,ll>> q;
q.pb({stx,sty});
while(q.size()){
auto k=q.front();q.pop_front();
for(ll i=0;i<4;i++){
ll x=k.fi+b[i],y=k.se+c[i];
if(s[x][y-1]=='*') continue;
if(x>0&&y>0&&x<=n&&y<=m&&dist[x][y]>dist[k.fi][k.se]+(s[x][y-1]!=s[k.fi][k.se-1])){
dist[x][y]=dist[k.fi][k.se]+(s[x][y-1]!=s[k.fi][k.se-1]);
if(!(s[x][y-1]!=s[k.fi][k.se-1]))q.push_front({x,y});
else q.pb({x,y});
}
}
}
}
int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);cout.tie(0);
// freopen("test.INP","r",stdin);
// freopen("test.OUT","w",stdout);
cin>>n>>m;
for(i=1;i<=n;i++){
cin>>s[i];
for(j=1;j<=m;j++)
dist[i][j]=INF;
}
dist[1][1]=1;
dfs(1,1);
for(i=1;i<=n;i++){
for(j=1;j<=m;j++){
if(dist[i][j]==INF) continue;
ans=max(ans,dist[i][j]);
}
}
cout<<ans;
return 0;
}
