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

using namespace std;

int a[803],n,s,dr,st,mijloc,rez,i,j;

int main()
{
    ifstream f("nrtri.in");
    ofstream g("nrtri.out");
    f>>n;
    for (i=1;i<=n;i++)
        f>>a[i];
    sort (a+1,a+n+1);
    for (i=1;i<=n-2;i++)
        for (j=i+1;j<=n-1;j++){
            s=a[j]+a[i];
            st=j;
            dr=n+1;
            while (dr-st!=1)
            {
                mijloc=(st+dr)/2;
                if (a[mijloc]<=s)
                    st=mijloc;
                else dr=mijloc;
            }
            rez=rez+st-j;
        }
    g<<rez;
    return 0;
}