#include <iostream>
#include <vector>
#include <bits/stdc++.h>
using namespace std;

const int maxn = 30005;
const int INF = 2e9;
int n, a[maxn];
int dp[maxn][4];
int rec(int at, int medal) {
if(at == n) {
return 0;
}
if(dp[at][medal] != -1) {
return dp[at][medal];
}
int res = INF;

if(medal == 1) {
for(int new_medal = 1; new_medal <= 3; new_medal++) {
int promena = 0;

if(medal != a[at]) {
promena = 1;
}
res = min(res, rec(at + 1, new_medal) + promena);
}
}
else if(medal == 2) {
for(int new_medal = 2; new_medal <= 3; new_medal++) {
int promena = 0;
if(medal != a[at]) {
promena = 1;
}

res = min(res, rec(at + 1, new_medal) + promena);
}
}
else {
int promena = 0;
if(medal != a[at]) {
promena = 1;
}
res = min(res, rec(at + 1, 3) + promena);
}

dp[at][medal] = res;
return res;
}
int main()
{
cin >> n;
for(int i = 0; i < n; i++) {
cin >> a[i];
}

memset(dp, -1, sizeof dp);
int res = INF;
for(int i = 1; i <= 3; i++) {
res = min(res, rec(0, i));
}

reverse(a, a + n);
memset(dp, -1, sizeof dp);
for(int i = 1; i <= 3; i++) {
res = min(res, rec(0, i));
}

cout << res << endl;

return 0;
}