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

using namespace std;

int n;

int Bsearch(int st,int dr,vector<int>v,int c)
{

    if (c>v.back())
        return n - 1;
    while ( st <= dr )
    {
        int m=st+(dr-st)/2;
        if(v[m]==c)
        {
            while(v[m+1]==v[m])
                m ++;
            return m;
        }
        if(v[m]>c)
             dr=m-1;
        else
            st=m+1;
    }
    return st - 1;
}



int main()
{

    ifstream f("nrtri.in");
    ofstream g("nrtri.out");
    int i,aux,j,nrtri=0;
    vector <int> v;
    f>>n;
    for(i=0;i<n;i++ )
    {
        f >> aux;
        v.push_back(aux);
    }
    sort(v.begin(),v.end());
    for (i=0;i<n-2;i++ )
        for ( j=i+1;j<n-1;j++ )
        {
            aux=Bsearch(j,n-1,v,v[i]+v[j]);
            nrtri+=(aux-j);
        }
    g<<nrtri;
    return 0;
}