#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin ("nrtri.in");
ofstream fout ("nrtri.out");
int n,i,j,u,p,mid,v[810],sol,ok1,ok2,k;
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++){
            p=j+1;
            u=n;
            k=0;
            while(p<=u){
                mid=(p+u)/2;
                if(v[i]+v[j]>=v[mid]){
                    k=mid-j;
                    p=mid+1;
                }
                else
                    u=mid-1;
            }
            sol+=k;
        }
    }
    fout<<sol;
    return 0;
}