#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int n, v[801], i, j, st, dr, mid, nr=0, aux;
int main(){
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i];
    sort(v,v+n+1);
    for(i=1;i<=n;i++){
        for(j=i+1;j<=n;j++){
            st=j;
            dr=n;
            aux=j;
            while(st<=dr){
                mid=(st+dr)/2;
                if(v[mid]<=v[i]+v[j]){
                    st=mid+1;
                    aux=mid;
                }else
                    dr=mid-1;
            }
            nr+=aux-j;
        }
    }
    fout<<nr;
    return 0;
}