#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int main()
{
    int n,v[2001],i,s=0,x,y,z;
    in>>n;
    for(i=1;i<=n;i++)
        in>>v[i];
    sort(v+1,v+n+1);
    for(y=n,x=n-1;y>2;y--,x--)
    {
        z=v[y]-v[x];
        int pos=1,msk;
        for(msk=n-2;msk>0;msk/=2)
            if(pos+msk<=n && v[pos+msk]<=z)
            pos+=msk;
        if(pos!=0)
            s=s+(x-pos);
    }
    out<<s-1;
    return 0;
}