#include<fstream>
#define inf "nrtri.in"
#define outf "nrtri.out"
#define NMax 802
using namespace std;

fstream f(inf,ios::in),g(outf,ios::out);

int N,nr;
int v[NMax];

void Citire()
{
f>>N;
for(int i=1;i<=N;i++)f>>v[i];
}

int cauta(int st,int dr,int num)
{
int mij,p;
bool gasit=false;
while(st<=dr)
    {
    mij=(st+dr)/2;
    if(num>=v[mij])
        {
        p=mij;
        st=mij+1;
        gasit=true;
        }
    else dr=mij-1;
    }
if(gasit)return p;
return -1;
}

void Rezolva()
{
int p;
sort(v+1,v+N+1);
for(int i=1;i<=N-2;i++)
    {
    for(int j=i+1;j<=N-1;j++)
        {
        p=cauta(j+1,N,v[i]+v[j]);
        if(p!=-1)nr+=(p-j);
        }
    }
g<<nr;
}

int main()
{
Citire();
Rezolva();
f.close();
g.close();
return 0;
}