#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin ("nrtri.in");
ofstream fout("nrtri.out");
int n,i,j,sol,V[801];
int caut(int st,int S)
{
    int mid,dr=n;
    while(st<=dr)
    {
        mid=(st+dr)/2;
        if(V[mid]<=S)
            st=mid+1;
        else
            dr=mid-1;
    }
    return dr;
}
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>V[i];

    sort(V+1,V+n+1);

    for(i=1;i<=n-2;i++)
    {
        for(j=i+1;j<=n-1;j++)
            sol=sol+caut(j+1,V[i]+V[j])-j;
    }
    fout<<sol;
    return 0;
}