#include <iostream>
#include <algorithm>
#include <fstream>
using namespace std;
ifstream fin("ntri.in");
ofstream fout("ntri.out");
int n,i,v[100000],st,dr,verif,s;
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
    {
        cin>>v[i];
    }
    sort(v,v+n+1);
    s=0;
    for(i=1;i<=n;i++)
    {
        st=1;
        dr=i-1;
        verif=0;
        while(verif==0)
        {
            if(v[st]+v[dr]>=v[i])
            {
                s++;
                dr--;
            }
            else if(v[st]+v[dr]<v[i])
            {
                st++;
            }
            if(st>dr)
            {
                verif=1;
            }
        }
    }
    fout<<s;
}