#include <bits/stdc++.h>
using namespace std;

int main()
{
    int n;
    cin>>n;
    int k[101];
    memset(k,0,sizeof(k));
    for (int i=0;i<n;i++)
    {
        cin>>k[i];
    }
    sort(k,k+n);
    int *begin,*end;
    int tot=0;
    for (int i=2;i<n;i++)
    {
        begin=&k[0],end=&k[i-1];
        while (begin<end)
        {
            if (*begin+*end>k[i])
                end--;
            else if (*begin+*end<k[i])
                begin++;
            else if (*begin!=*end)
            {
                end--;
                begin++;
                tot++;
            }
        }
    }
    cout<<tot;
    return 0;
}