#include <fstream>
#include <algorithm>
using namespace std;
ifstream cin ("nrtri.in");
ofstream cout ("nrtri.out");
int v[805];
int cautarebinaraa(int s, int n, int start){
    int st=start+1,dr=n,res=-1;
    while(st<=dr){
        int mij=(st+dr)/2;
        if(v[mij]<=s){
            res=mij;
        st=mij+1;
        }
        else
        dr=mij-1;
    }
    if(res==-1)
    return 0;
    return res-start;
}
int main()
{
    int n,cnt=0;
    cin>>n;
    for(int i=1;i<=n;i++)
    cin>>v[i];
    sort(v+1,v+n+1);
    for(int i=1;i<n;i++)
    for(int j=i+1;j<=n;j++){
    cnt+=cautarebinaraa(v[i]+v[j],n,j);
    }
    cout<<cnt;
    return 0;
}