#include <fstream>
#include <algorithm>

using namespace std;

fstream in("nrtri.in");
fstream out("nrtri.out");

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

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