#include<fstream>
#include<algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int n,i,j,a[1001],nr;
int bin(int st,int dr,int z)
{
    int mij;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(a[mij]<=z)
        st=mij+1;
        else
        dr=mij-1;
    }
    return dr;
}
int main()
{
    f>>n;
    for(i=1;i<=n;i++)
        f>>a[i];
    sort(a+1,a+n+1);
    for(i=1;i<=n-1;i++)
    for(j=i+1;j<=n;j++)
    nr=nr+bin(i,n,a[i]+a[j])-j;
    g<<nr;
    return 0;
}