#include <algorithm>
#include <fstream>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int n,x,v[801],i,mij,st,dr,sol,j;
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++)
    {
        x=v[i]+v[j];
        st=j+1;
        dr=n;
        while(st<=dr)
        {
            mij=(st+dr)/2;
            if(x>v[mij])
                dr=mij-1;
            else
                st=mij+1;
        }
        sol+=dr-j;
    }
    g<<sol;
    return 0;
}