#include <fstream>
#include <algorithm>
using namespace std;

ifstream f("nrtri.in");
ofstream g("nrtri.out");

short n, nr, st, dr, m;
int LG[30001], i, j, k;

int main()
{
    f >> n;

    for (i = 1; i <= n; i++)
        f >> LG[i];

    sort (LG+1, LG+n+1);
    nr = 1;
    for (i = 1; i < n; i++)
        for (j = i+1; j <= n; j++)
        {
            st = i, dr = j;
            while (st <= dr)
            {
                m = (st+dr)/2;
                if (LG[dr] < LG[m] + LG[st])
                    st = m+1;
                else
                    dr = m-1;
            }
            if (LG[dr] == LG[m]+LG[st])
                nr++;
        }
    g << nr << "\n";
//    g << M_PI;
    return 0;
}