#include<bits/stdc++.h>
#define nmax 2005
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int  a[nmax],n;
inline void Citire()
{
    int i;
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>a[i];
    sort(a+1,a+n+1);
}
inline int CautBin(int capat,int x)
{
    int st=capat,dr=n,mij,poz=0;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(a[mij]>=x)
        {
            poz=mij;
            st=mij+1;
        }
        else dr=mij-1;
    }
    return poz;
}
inline void Rezolvare()
{
    int i,j,sol=0;
    for(i=1;i<n-1;i++)
        for(j=i+1;j<=n-1;j++)
            if(CautBin(j+1,a[i]+a[j])!=0)
            sol+=CautBin(j+1,a[i]+a[j])-(j+1)+1;
        fout<<sol<<"\n";
}
int main()
{
    Citire();
    Rezolvare();
    fin.close();
    fout.close();
    return 0;
}