#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;
}