#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<cstring>
#include<string>
#include<ctime>
#include<cmath>
#include<algorithm>
#include<cctype>
#include<iomanip>
using namespace std;
int n,ans;
int a[300003];
int f[300003][3],g[300003][3];
int main()
{
memset(f,0x7,sizeof(f));
memset(g,0x7,sizeof(g));
cin>>n;
for(int i=1;i<=n;i++)
cin>>a[i];
for(int i=1;i<=3;i++)
f[0][i]=g[0][i]=0;
for(int i=1;i<=n;i++)
for(int j=1;j<=3;j++)
for(int k=1;k<=3;k++)
{
if(j>=k)
f[i][j]=min(f[i][j],f[i-1][k]+(j!=a[i]));
if(j<=k)
g[i][j]=min(g[i][j],g[i-1][k]+(j!=a[i]));
}
ans=1000000000;
for(int i=1;i<=3;i++)
ans=min(ans,min(f[n][i],g[n][i]));
cout<<ans<<endl;
return 0;
}
for(int i=1;i<=n;i++)
for(int j=1;j<=3;j++)
for(int k=1;k<=3;k++)
{
if(j>=k)
f[i][j]=min(f[i][j],f[i-1][k]+(j!=a[i]));
if(j<=k)
g[i][j]=min(g[i][j],g[i-1][k]+(j!=a[i]));
}
其中的j!=a[i]是什么意思?