#include <bits/stdc++.h>
using namespace std;
#define ll long long
int main(){
    ios_base::sync_with_stdio(0);
    int n;
    cin>>n;
    int ok =0;
    int ret=0;
    for (int i=0;i<n;i++) {
        int x;
        cin>>x;
        ok |= (1<<x);
        if (ok==3) ret++, ok=0;
    }
    cout<<ret<<endl;
}