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

const int NMAX=800;
int v[NMAX+1];
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int CautareBinara(int p1, int p2, int n)
{
    int st=p2+1, dr=n, sol = -1;
    int m;
    int x=v[p1]+v[p2];
    while(st<=dr)
    {
        m=(st+dr)/2;
        if(v[m]>x)
            dr=m-1;
        else
        if(v[m]<=x)
        {
            sol=m;
            st=m+1;
        }
    }
    return sol;
}

int main()
{
    int n,i,x,j,cnt=0;
    fin>>n;
    for(i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    sort(v+1,v+n+1);
    for(i=1;i<=n-2;i++)
    {
        for(j=i+1;j<=n-1;j++)
        {
            x=CautareBinara(i,j,n);
            if(x!=-1)
                cnt+=x-j;
        }
    }
    fout<<cnt;
    return 0;
}