#include <fstream>
#include <stdio.h>
using namespace std;
FILE *fin=fopen("nrtri.in","r");
ofstream fout("nrtri.out");
int n,m,i,x,st,dr,poz,j,v[802],start,ultimul;
long long mid,suma,sol;
short q;
int main()
{
    fscanf(fin,"%d",&n);
    for(i=1; i<=n; i++)
        fscanf(fin,"%d",&v[i]);
    for(i=1; i<n; i++)
        for(j=i+1; j<=n; j++)
            if(v[j]<v[i])
                swap(v[i],v[j]);
    for(i=1; i<n-1; i++)
        for(j=i+1; j<n; j++)
        {
            suma=v[i]+v[j];
            start=j+1;
            if(v[i]==v[j] && v[j]==v[j+1])
            { ///cautam primul elem diferit de v[j];
                st=j+1;
                dr=n;
                while(st<=dr)
                {
                    mid=(st+dr)/2;
                    if(v[mid]==v[j])
                    {
                        start=mid;
                        st=mid+1;
                    }
                    else dr=mid-1;
                }
            }
          ///cautam ultimul elem cu propr c<=a+b
          st=j+1;dr=n;
          while(st<=dr)
          {
              mid=(st+dr)/2;
              if(v[mid]>suma)
                dr=mid-1;
              else{
                st=mid+1;
                ultimul=mid;
              }
          }
          sol+=ultimul-start+1;
        }
        fout<<sol;
    return 0;
}