#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
int v[1000];
int cautare_binara(int n, int x, int s);
int main()
{
    ifstream in("nrtri.in");
    ofstream out("nrtri.out");
    int n,nr=0,s,k;
    in>>n;
    for(int i=1; i<=n; i++)
        in>>v[i];
    sort(v+1,v+1+n);
    for(int i=1; i<=n-2; i++)
    {
        for(int j=i+1; j<=n-1; j++)
        {
         s=v[i]+v[j];
         k=cautare_binara(j+1,n,s);
         nr=nr+(k-j);
        }
    }
    out<<nr;
    return 0;
}
int cautare_binara(int st, int dr, int s)
{
    int mij;
    while(dr>=st)
    {
        mij=(dr+st)/2;
        if(v[mij]>s)
        {
            dr=mij-1;
        }
        else
        {
            st=mij+1;
        }
    }
    return st-1;
}