#include <fstream>
#include <algorithm>

using namespace std;
int n, i, x, nr, v[803], j, st, dr, mid;
int main()
{
    ifstream fin("nrtri.in");
    ofstream fout("nrtri.out");
    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++){
            x=v[i]+v[j];
            st=j+1;
            dr=n;
            while(st<=dr){
                mid=(st+dr)/2;
                if(v[mid]>x)
                    dr=mid-1;
                else{
                    st=mid+1;
                }
            }
            nr+=st-j-1;
        }
    fout<<nr;
    return 0;
}