#include <iostream>
#include <algorithm>
#include <fstream>
using namespace std;
int i,j,n,v[805],sol,k;
int main()
{
ifstream f("nrtri.in");
ofstream g("nrtri.out");
    f>>n;
    for (i=1;i<=n;i++)
        f>>v[i];
    sort(v+1,v+n+1);
    for (i=1;i<=n;i++) {
            k=i+1;
        for (j=i+1;j<=n;j++) {
          while (k<n && v[k]<v[i]+v[j])
            k++;
            if (v[k]==v[i]+v[j]) {sol+=k-j, k++;
            else if (v[k]>v[i]+v[j])
            sol+=k-j-1, k++;
        }
    }
    g<<sol;
}