#include <cstdio>
#include <algorithm>
#include <cstdio>
using namespace std;
int n,i,j,v[8005],p,nr;
int caut(int stg, int dr, int s)
{
    int mijloc;
    int primul;
    primul=1;
    int poz;

    while(stg<=dr)
    {
        mijloc=(stg+dr)/2;
        if((v[mijloc]<=s&&v[mijloc+1]>s)||(v[mijloc]<=s&&mijloc==n))
            return 1;
        else
        if(v[mijloc]<=s&&v[mijloc+1]<=s)
            stg=mijloc+1;
        else
            dr=mijloc-1;

    }
    mijloc=(stg+dr)/2;
    if(v[mijloc]<s||v[mijloc]>s)
        return 0;
    return 1;

}
int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    scanf("%d",&n);
    for(i=1;i<=n;i++)
        scanf("%d",&v[i]);
    sort(v+1,v+n+1);
  for (i=1; i<=n; i++)
    for (j=i+1; j<=n; j++)
     {
         int s=v[i]+v[j];
         nr+=caut(j+1,n,s);
     }
     printf("%d",nr);

    return 0;
}