#include <bits/stdc++.h>
#define N 100005
using namespace std;

long long n, a[N];

void sub1()
{
    long long cnt = 0;
    for(int i = 1; i <= n; i++)
    {
        if(a[i] + a[i+1] > a[n]) break;
        for(int j = i + 1; j <= n; j++)
        {
            if(a[i] + a[j] > a[n]) break;
            if(binary_search(a + j + 1, a + 1 + n, a[i] + a[j]))
            {
                //cout << a[i] << ' ' << a[j] << '\n';
                cnt++;
            }
        }
    }
    cout << cnt * 2;
}

int main()
{
    cin.tie(0) -> sync_with_stdio(false);
    freopen("BAI2.INP", "r", stdin);
    freopen("BAI2.OUT", "w", stdout);

    cin >> n;
    for(int i = 1; i <= n; i++) cin >> a[i];
    sort(a + 1, a + 1 + n);
    if(n <= 3000) sub1();
    else
    {
        long long cnt = 0;
        for(int i = 1; i <= n; i++)
        {
            int j = lower_bound(a + 1, a + 1 + n, a[n] - a[i]) - a;
            if(a[j] <= a[i]) break;
            cnt += j - i;
        }
        cout << cnt * 2;
    }
    return 0;
}