#include <fstream>
#include <algorithm>
using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int st,dr,i,j,n,mid,a[1000],sum;
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>a[i];

    sort(a+1,a+n+1);

    for(i=1;i<=n-2;i++)
        for(j=i+1;j<=n-1;j++){
            st=j+1;dr=n;
            while(st<=dr){
                mid=(st+dr)/2;
                if(a[mid]<=a[i]+a[j])
                    st=mid+1;
                else
                    dr=mid-1;
            }
            sum=sum+dr-j;
        }
    fout<<sum;
    return 0;
}