#include <fstream>
#include <algorithm>

using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int v[801],s[320001],S,n,t;

//Pentru ca segmentele de lungimi a,b,c sa formeze un triunghi:  med(a,b,c) + min(a,b,c) >= max(a,b,c)

int bynary_search (int  lo, int hi, int x)
{
    if (hi-lo<=1)
    {
        for (;s[hi]>=x; hi--);
        return hi;
    }
    int mid=(lo+hi)/2;
    if (x<=s[mid]) return bynary_search (lo,mid,x);
    else return bynary_search (mid+1,hi,x);
}

int main()
{
    fin>>n;
    for (int i=1; i<=n; i++) fin>>v[i];

    for (int i=1; i<=n; i++)
        for (int j=i+1; j<=n; j++)
        s[++t]=v[i]+v[j];

    sort (s+1,s+t+1);

    for (int i=1; i<=n; i++)
    {
         S += bynary_search (0,t+1,v[i]);   //invariant left < x <= right
    }
    fout<<S;
}