#include <iostream>
#include <fstream>
#include <algorithm>

using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

const int NMAX=805;
int v[NMAX];

int cautbin(int st,int dr,int s)
{
    int rasp=-1;
    while(st<=dr)
    {
        int mij=(st+dr)/2;
        if(v[mij]<=s)
        {
            rasp=mij;
            st=mij+1;
        }
        else
            dr=mij-1;
    }
    return rasp;
}
int main()
{
    int n,nrtri=0,i,j,kon,s,a;
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<n;i++)
        for(j=i+1;j<=n;j++)
        {
            s=v[i]+v[j];
            a=cautbin(j+1,n,s);
            if(a==-1)
                kon=0;
            else
                kon=a-j;
            nrtri=nrtri+kon;
        }
    fout<<nrtri;
    return 0;
}