#include <fstream>
#include <algorithm>



using namespace std;


ifstream in("nrtri.in");
ofstream out("nrtri.out");


const int  L=9;
const int N=801;
int v[N];

int main()

{

        int n, r, nr = 0, pas;
        in>>n;
        for(int i=1;i<=n;i++){
            in>>v[i];
        }
        sort(v+1,v+n+1);
        for(int i=1;i<=n;i++){
            r = 0;
            pas = 1<<L;
            int j=i+1;
            for(j=i+1;j<n;j++){
                while(pas!=0){
                    if(r+pas<=n && v[r+pas]<=v[i]+v[j]){
                        r+=pas;
                    }
                    pas/=2;
                }
                if(r!=0){
                    nr=nr+r-j;
                }
            }
        }
        out<<nr;
        return 0;
}