#include <iostream>
#include <fstream>
using namespace std;
int v[801];
int n;
int cautbin(int st,int dr,int x)
{
    if (x<v[st])
        return 0;
    int mij,poz=0;
    while (st<=dr)
    {
        mij=(st+dr)/2;
        if (v[mij]<=x)
        {
            poz=mij;
            st=mij+1;
        }
        if (v[mij]>x)
            dr=mij-1;
    }
    return poz-st+1;
}
int main()
{
    ifstream in("nrtri.in");
    ofstream out("nrtri.out");
    in>>n;
    int i;
    int s=0;
    for (i=1;i<=n;i++)
    {
        in>>v[i];
    }
    int j;
    for (i=1;i<=n-2;i++)
    {
        for (j=j+1;j<=n-1;j++)
        {
            s=s+cautbin(j+1,n,v[j]+v[i]);
        }
    }
    cout<<s;
}