#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

vector<int> v;
int n,s=0;

int cautbin(int suma, int poz)
{
    int st = poz+1, dr = n, m, last = -1;

    while(st<=dr)
    {
        m = (st+dr) / 2;
        if(v[m] <= suma)
        {
            last = m;
            st = m + 1;
        }
        else
        {
            dr = m - 1;
        }
    }

    if(last!= - 1) return last - poz;
    else return 0;

}

void read()
{
    ifstream f ("nrtri.in");
    f>>n;
    v.resize(n+1);
    for (int i=1; i<=n; ++i)
        f>>v[i];
}

int partition(int low,int high)
{
    int mid=(low+high)/2,pivot=v[mid],i=low-1,j=high+1;
LOOP:
    do ++i;
    while (v[i]<pivot);
    do --j;
    while (v[j]>pivot);
    if (i>=j)
        return j;
    swap(v[i],v[j]);
    goto LOOP;
}

void quicksort(int low,int high)
{
    if (low<high)
    {
        int pivot=partition(low,high);
        quicksort(low,pivot);
        quicksort(pivot+1,high);
    }
}

void solve()
{
    quicksort(1,n);
    for (int i=1; i<n; ++i)
        for (int j=i+1; j<=n; ++j)
            s+=cautbin(v[i]+v[j],j);
}

int main()
{
    read();
    solve();
    ofstream t ("nrtri.out");
    t<<s;
    return 0;
}