#include <fstream>
#include <algorithm>
using namespace std;
ifstream cin("nrtri.in");
ofstream cout("nrtri.out");
int main()
{
    int n,i,j,v[805],s,c=0,k,p;
    cin>>n;
    for(i=1;i<=n;i++)
        cin>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<n-1;i++)
    {
        for(j=i+1;j<n;j++)
        {
            s=v[i]+v[j];
            int st=j+1,dr=n,m;
            p=j;
            while(st<=dr)
            {
                m=(st+dr)/2;
                if(v[m]<=s)
                {
                    p=m;
                    st=m+1;
                }
                else
                    dr=m-1;
            }
            c+=p-j;
        }
    }
    cout<<c;
    return 0;
}