#include<fstream>
#include<algorithm>
using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int n,sol,a[803];
int main()
{
    in>>n;
    for(int i=1; i<=n; i++)
        in>>a[i];
    sort(a+1,a+n+1);
    for(int i=1; i<n-1; i++)
        for(int j=i+1; j<n; j++)
        {
            int m,p=1+j,u=n,poz=-1;
            int x=a[i]+a[j];
            while(p<=u)
            {
                m=(p+u)/2;
                if(a[m]<=x)p=m+1;
                else u=m-1;
            }
            sol+=u-j;
        }
    out<<sol<<'\n';
    out.close();
    return 0;
}