#include <fstream>
#include <algorithm>
using namespace std;
ifstream cin("nrtri.in");
ofstream cout("nrtri.out");
int n,v[2000];
int cb(int x)
{
    int st=0,dr=n-1;
    while(st<=dr)
    {
    int mij=(st+dr)/2;
    if(v[mij]>x){dr=mij-1;}
    else st=mij+1;
    }
    return dr;
}
int main()
{
    int i,j,k=0;
    cin>>n;
    for(i=0;i<n;i++)
        cin>>v[i];
    sort(v,v+n);
    for(i=0;i<n-2;i++)
        for(j=i+1;i<n-1;j++)
        k+=cb(v[i]+v[j])-j;
        cout<<k;
    return 0;
}