#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]);
    v[n+1]=40000;
    for(i=1; i<n-1; i++)
        for(j=i+1; j<n; j++)
        {
            suma=v[i]+v[j];
            st=j+1;dr=n; ultimul=0;
            while(st<=dr)
            {
                mid=(st+dr)/2;
                if(v[mid]<=suma && v[mid+1]>suma)
                {
                    ultimul=mid;
                    break;
                }
                else if(v[mid]<=suma)
                    st=mid+1;
                else dr=mid-1;
            }
           if(ultimul!=0) sol+=ultimul-j;
        }
    fout<<sol;
    return 0;
}