#include<iostream>
#include<fstream>
#include<algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int v[805];
int main()
{
    int n;
    int suma=0;
    fin>>n;
    for (int i=0; i<n; i++)
    {
        fin>>v[i];
    }
    sort(v,v+n);
    for (int i=0; i<n-2; i++)
    {
        for (int k=i+1; k<n-1; k++)
        {
            int x=v[i]+v[k];

            int s=k+1;
            int d=n-1;
            int sol=0;
            while(s<=d)
            {
                int mij=(s+d)/2;
                if (x>=v[mij])
                {
                    sol=mij;
                    s=mij+1;
                }
                else
                {
                    d=mij-1;
                }
            }

            if (sol!=0)
            {
                suma=suma+sol-k;
            }
        }
    }
    fout<<suma;
}