#include<fstream>
#include<algorithm>
using namespace std;
int a[810],n,nr,s;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
void citire()
{
    int i;
    f>>n;
    for(i=1;i<=n;i++)
        f>>a[i];
}
int cautarebinara(int st,int dr,int x)
{
    int gasit=0,m;
    while(st<=dr&&gasit==0)
    {
        m=(st+dr)/2;
        if(a[m]<=x&&a[m+1]>x)
            return m;
        else
            if(a[m]<=x)
                st=m+1;
            else
                dr=m-1;
    }
        return -1;
}
void calculeaza()
{
    int  i,j,c;
    s=0;
    sort(a+1,a+n+1);
    a[n+1]=9999999;
    for(i=1;i<=n-2;i++)
        for(j=i+1;j<=n-1;j++)
        {
            s=a[i]+a[j];
            c=cautarebinara(j+1,n,s);
            if(c>j)
                nr=nr+c-j;
    }
}
int main()
{
    citire();
    calculeaza();
    g<<nr;
    return 0;
}