#include <iostream>
#include <bits/stdc++.h>
#include <vector>
using namespace std;
const int maxn = 30005;
const int INF = 2e9;
int n;
int 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;
    for(int current_medal = medal; current_medal <= 3; current_medal++) {
        int cost = 0;
        if(A[at] != medal) {
            cost = 1;
        }

        for(int next_medal = medal; next_medal <= 3; next_medal++) {
            res = min(res, rec(at + 1, next_medal) + cost);
        }
    }
    dp[at][medal] = res;
    return res;
}
int main() {
    ios_base::sync_with_stdio(false);
    cin >> n;

    for(int i = 0; i < n; i++) {
        cin >> A[i];
    }

    int res = INF;
    memset(dp, -1, sizeof dp);
    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;
}