#include<cstdio>
#include<algorithm>
using namespace std;
int n,v[805],nr;
int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    scanf("%d",&n);
    for(int i=1;i<=n;i++) scanf("%d",&v[i]);
    sort(v+1,v+n+1);
    for(int i=1;i<=n;i++)
    {
        for(int j=i+1;j<=n;j++)
        {
            int s=v[i]+v[j];
           int x=upper_bound(v+1,v+n+1,s-1)-v;
          while (v[x]==s && x<=n) x++;
          if (x<=n) nr=nr+(n-x+1);
        }
    }
    printf("%d\n",nr);
    return 0;
}