#include <iostream>
#include <fstream>
#include <algorithm>
#define NMax 801
///#define f cin
///#define g cout
using namespace std;

int n, a[NMax], x, ans;

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

int cautare_binara(int a[NMax], int n, int x)
{
    int L = 0;
    int R = n - 1;
    while(L <= R)
    {
        int mid = (int)(L + R)/2;
        if(a[mid] < x) L = mid + 1;
        else if(a[mid] >= x)
        {
            return mid;
            R = mid - 1;
        }
    }
    return -1;
}

int main()
{
    ios::sync_with_stdio(false);
    f >> n;
    for(int i = 0; i < n; ++i)
        f >> a[i];
    sort(a, a + n);
    for(int i = 0; i < n - 1; ++i)
        if(cautare_binara(a, n, a[i] + a[i + 1]) != -1) ++ans;
    g << ans << '\n';
    return 0;
}