#include <iostream>
using namespace std;

int a,
    u,
    f,
    arr[100][4];

int main()
{

 cin >> a;
 for(int i = 0; i < a; i++)
 {
     cin >> arr[i][i];
     f += arr[i][i] %  10;
          arr[i][i] /= 10;
     f += arr[i][i] %  10;
          arr[i][i] /= 10;
     f += arr[i][i] %  10;
 }

 cout<< f / 3;
}