#include<fstream>
#include<algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int n,a[1001];
void citire()
{
    int i;
    f>>n;
    for(i=1;i<=n;i++)
        f>>a[i];
    sort(a+1,a+n+1);
}
int cauta(int inc,int sf,int k)
{
    int m;
    while(inc<=sf)
    {
        m=(inc+sf)/2;
        if(k==a[m])
           return m;
        if(k>a[m])
            inc=m+1;
        else
            sf=m-1;
    }
    return sf;
}
void solve()
{
    int i,j,sol=0,poz;
    for(i=1;i<n-1;i++)
        for(j=i+1;j<n;j++)
        {
            poz=cauta(j+1,n,a[i]+a[j]);
            sol+=poz-j;

        }
    g<<sol<<'\n';
}
int main(){

    citire();
    solve();
return 0;
}