#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int v[810],n,i,j,st,dr,sol;
int main(){
    fin>>n;
    for (i=1;i<=n;i++)
        fin>>v[i];

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

    for (i=1;i<n-1;i++)
        for (j=i+1;j<n;j++) {
            st = j+1;
            dr = n;
            while (st <= dr) {
                int mid=(st+dr)/2;
                if (v[mid]>v[i]+v[j])
                    dr=mid-1;
                else
                    st=mid+1;
            }
            sol += dr-j;
        }
    fout<<sol;

    return 0;
}