#include <iostream>
#include <algorithm>
using namespace std;
int n;
int niza[30005];
int dp[30005][3];
int rec(int i, int prev_medal) {
    if(i == n) {
        return 0;
    }
    if(dp[i][prev_medal] != -1) {
        return dp[i][prev_medal];
    }
    int result = 2e9;
    if(prev_medal == 0) {
        result = min(result, rec(i + 1, 0) + (niza[i] != prev_medal));
        
    }
    else if(prev_medal == 1) {
        result = min(result, rec(i + 1, 1) + (niza[i] != prev_medal));
        result = min(result, rec(i + 1, 0) + (niza[i] != prev_medal));
        
    }
    else if(prev_medal == 2) {
        result = min(result, rec(i + 1, 2) + (niza[i] != prev_medal));
        result = min(result, rec(i + 1, 1) + (niza[i] != prev_medal));
        result = min(result, rec(i + 1, 0) + (niza[i] != prev_medal));
    }
    dp[i][prev_medal] = result;
    return result;
}
int main()
{
    cin >> n;
    for(int i = 0; i < n; i++) {
        cin >> niza[i];
        niza[i]--;
        dp[i][0] = dp[i][1] = dp[i][2] = -1;
    }
    int answer = 2e9;
    for(int i = 0; i <= 2; i++) {
        answer = min(answer, rec(0, i));
    }
    for(int i = 0; i < n; i++) {
        dp[i][0] = dp[i][1] = dp[i][2] = -1;
    }
    reverse(niza, niza + n);
    for(int i = 0; i <= 2; i++) {
        answer = min(answer, rec(0, i));
    }
    cout << answer << endl;
    return 0;
}