#include <fstream>
#include <algorithm>
using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int n,i,j,st,dr,mid,sol,v[801];

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

    fout<<sol;

    return 0;
}