#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int v[1003],n,s,nr,i,j;
int st,dr,mid;
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<=n-2;i++)
        for(j=i+1;j<=n-1;j++){
            s=v[i]+v[j];
            st=j+1;
            dr=n;
            while(st<=dr){
                mid=(st+dr)/2;
                if(v[mid]>s)
                    dr=mid-1;
                else
                    st=mid+1;
            }
        nr=nr+dr-j;
        }
    fout<<nr;

    return 0;
}