#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, a = 0, b = 0, ans = 0, mid;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> mid;
    if (mid == 2)
      a++;
    else
      b++;
  }
  if (a > b)
    ans = b;
  else {
    ans = a;
    b = b - a;
    ans += b / 3;
  }
  cout << ans << endl;
  return 0;
}
