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

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

int n,ans;
int v[2005];

int bs(int arg)
{
    int st,med,dr,last;
    st=1; dr=n;
    while(st<=dr)
    {
        med=(st+dr)/2;
        if(v[med]>arg || v[med]==arg) dr=med-1;
        else
        {
            last=med;
            st=med+1;
        }
    }
    return last;
}
int main()
{
    in>>n;
    for(int i=1; i<=n; i++) in>>v[i];
    sort(v+1,v+n+1);

    for(int i=1; i<n; i++)
        for(int j=i+1; j<=n; j++)
        {
            ans+=bs(v[i]+v[j]);
            ans-=j;

        }
    out<<ans;
    return 0;
}