#include<fstream>
#include<algorithm>
using namespace std;
int v[1000];
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int main ()
{
    int n,x,y,pos,msk,a,s=0,i,j;
    in>>n;
    for(int i=1; i<=n; i++){
        in>>v[i];
    }
    sort(v+1,v+n+1);
    i=n;
    j=i-1;
    while(j>1)
    {
        x=v[i];
        y=v[j];
    a=x-y;
    pos=0;
    for(msk=1<<20;msk>0;msk/=2)
        if(pos+msk<=n && v[pos+msk]<=a)
        pos+=msk;
        if(pos!=0)
        {s+=j-pos;}
        i--;
        j--;
    }
    out<<s;
    return 0;
}