#include 
#include 
#include 
using namespace std;
int dp[30005][3];
int main()
{
    int n;
    cin >> n;
    vector v(n);
    for(int i = 0; i < n; i++) {
        cin >> v[i];
        v[i]--;
        dp[i][0] = dp[i][1] = dp[i][2] = 2e9;
    }
    int result = 2e9;
        dp[0][0] = (v[0] != 0);
        dp[0][1] = (v[0] != 1);
        dp[0][2] = (v[0] != 2);
       
        for(int i = 1; i < n; i++) {
            for(int j = 0; j <= 2; j++) {
                for(int k = 0; k <= j; k++) {
                    dp[i][k] = min(dp[i][k], dp[i - 1][j] + (v[i] != k));
                }
            }
        }
        
    result = min(result, dp[n - 1][0]);
    result = min(result, dp[n - 1][1]);
    result = min(result, dp[n - 1][2]);
    
    for(int i = 0; i < n; i++) {
        
        dp[i][0] = dp[i][1] = dp[i][2] = 2e9;

    }
        reverse(v.begin(), v.end());
        dp[0][0] = (v[0] != 0);
        dp[0][1] = (v[0] != 1);
        dp[0][2] = (v[0] != 2);
       
        for(int i = 1; i < n; i++) {
            for(int j = 0; j <= 2; j++) {
                for(int k = 0; k <= j; k++) {
                    dp[i][k] = min(dp[i][k], dp[i - 1][j] + (v[i] != k));
                }
            }
        }
    
    result = min(result, dp[n - 1][0]);
    result = min(result, dp[n - 1][1]);
    result = min(result, dp[n - 1][2]);
    
    cout << result << endl;
    return 0;
}