#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int v[805],i,n,j,cont,st,dr,mij,s,val;
int main()
{
    f>>n;
    for(i=1;i<=n;i++)
        f>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<=n-2;i++)
    {
        for(j=i+1;j<=n-1;j++)
        {
            st=j+1;
            dr=n;
            s=v[i]+v[j];
            val=j;
            while(st!=dr)
            {
                mij=(st+dr)/2;
                if(s<=v[mij])
                {
                    dr=mij-1;
                }
                else
                {
                    st=mij+1;
                    val=mij;
                }
            }
            cont=cont+val-j;
        }
    }
    g<<cont;
    return 0;
}