#include <bits/stdc++.h>   using namespace std;   int n, d, res;   int a[200005];   int main() {     cin >> n;     for (int i = 1; i <= n; ++i) {       cin >> a[i];       if (a[i] == 2) d++;     }     if (d <= n / 2) {       res += d;       n -= 2 * d;       res += n / 3;       cout << res;       return 0;     } else {       cout << n - d;     }   }   