#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int n,j,i,x,tri,a[801],k,s;
int main()
{
    fin>>n;
    for (i=1;i<=n;i++)
        fin>>a[i];
    sort (a+1,a+n+1);
     i=1;
     j=2;
     while (i<n-1)
     {
      s=a[i]+a[j];
      x=upper_bound(a+1,a+n+1,s)-a;
      x--;
        if (x!=j) tri+=x-j;
      j++;
       if (j==n) {i++;j=i+1;}
     }
     fout<<tri<<'\n';
    return 0;
}