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

using namespace std;

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

int verif(int a,int b ,int c)
{
    if((a+b)>=c&&(a+c)>=b&&(b+c)>=a)
        return 1;
    return 0;
}

int main()
{
    int n;
    fin>>n;
    int v[n+1];
    for(int i=0;i<n;i++)
        fin>>v[i];
    sort(v,v+n);
    int i=0,k=0;
    while(n-1-i)
    {
        int st=0,dr=n-1,mij;
        while(st<=dr)
        {
           mij=(st+dr)/2;
           if(verif(v[i],v[n-i-1],v[mij]))
                k++,st=dr+5;
           else if(v[mij]>v[i]+v[n-i-1])
                dr=mij-1;
           else
                st=mij+1;
        }
        i++;
    }
    fout<<k-1;
}