/// Craciun Catalin
///  Nrtri
///   Cautare binara
///    www.infoarena.ro/problema/nrtri
#include <fstream>
#include <iostream>
#include <algorithm>

#define NMax 850
#define sizeMax 800000

using namespace std;

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

int n;
int A[NMax];
char intrare[sizeMax], *pointerTo=intrare;
long long tri=0;
int i,j;

inline int atoi()
{
    int x=0;

    for (;!(*pointerTo>='0' && *pointerTo<='9'); ++pointerTo);
    for (; (*pointerTo>='0' && *pointerTo<='9'); ++pointerTo)
        x=x*10+(*pointerTo-'0');

    return x;
}

void parcurgere()
{
    sort(A, A+n);
    if (0)
    {
        for (i=0;i<n-2;i++)
            for (j=i+1;j<n-1;j++)
                for (int k=j+1;k<n;k++)
                    if (A[i]+A[j]>=A[k] && A[j]+A[k]>=A[i] && A[i]+A[k]>=A[j])
                        tri++;
                    else
                        break;
    }
    else
    {
        for (int i=0;i<n-2;i++)
            for (int j=i+1;j<n-1;j++)
            {
                /// Cautare binara
                int k, pas, sol;
                for (k=1;2*k<=A[i]+A[j];k*=2){}
                sol=j;
                for (pas=k;pas>0;pas/= 2)
                    if (sol+pas<n && A[sol+pas]<=A[i]+A[j])
                        sol+=pas;
                tri+=sol-j;
            }
    }
    g<<tri<<'\n';
    g.close();
}

void citire()
{
    /// Citire optimizata cu atoi
    f.read(intrare, sizeMax);
    n=atoi();
    for (int i=0;i<n;i++)
        A[i]=atoi();
}

int main()
{
    citire();
    parcurgere();

    return 0;
}