#include <iostream>
#include <algorithm>
using namespace std;
int n,i,v[1000],m,p,u,k,j,s;
int main()
{
    cin>>n;
    for(i=1; i<=n; i++)
    {cin>>v[i];}
    sort (v+1,v+n+1);
    for(i=1;i<=n-2;i++)
    {
         for(j=i+1;j<=n-1;j++)
         {
             p=i+j;
             u=n;
             s=v[i]+v[j];
             while(p<=u)
             {
                 m=(p+u)/2;
                 if(s>v[m]) {p=m+1;}
                 else {u=m-1;}}
                 k=k+u-j;
             }

                      }
                      cout<<k;
                      return 0;
}