#include <fstream>
#include <algorithm>
using namespace std;
ifstream cin("nrtri.in");
ofstream cout("nrtri.out");
int n,m,i,j,k,s,rez,st,dr,mid;
int v[810];
int main () {
    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];
            st=j+1;
            dr=n;
            while (st<=dr) {
                mid=(st+dr)/2;
                if (v[mid]>s) {
                    dr=mid-1;
                }
                else {
                    st=mid+1;
                    rez++;
                }
            }
        }
    }
    cout<<rez;
}