#include <fstream>
#include <algorithm>

using namespace std;
long long int n,v[800],c;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
unsigned long long int cautare_binara(int x,int z)
{
    int st,dr,m;
    st=z+1;
    dr=n-1;
    while(st<=dr)
    {
        m=(st+dr)/2;
        if(v[m]<=x)
            st=m+1;
        else
            dr=m-1;
    }
    return dr-z;

}
int main()
{
    int i,j;
    f>>n;
    for(i=0;i<n;i++)
        f>>v[i];
    sort(v,v+n);

    for(i=0;i<n-2;i++)
        for(j=i+1;j<n-1;j++)
            c+=cautare_binara(v[i]+v[j],j);
    g<<c<<'\n';

    return 0;
}