#include<cstdio>
#include<algorithm>
#include<vector>
using namespace std;
vector<int>v;
int n;
vector<int>:: iterator it;
int bs(int a, int b)
{
    int st=b+1,dr=n,val,sum=v[a]+v[b],help;
    it=upper_bound(v.begin()+b,v.end(),sum);
    int ind=(int)(it-v.begin());
    help=ind-b-1;
    return help;
}
int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    int i,j,x;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&x);
        v.push_back(x);
    }
    sort(v.begin(),v.end());
    int sum=0;
    for(i=0;i<v.size()-2;i++)
    {
        for(j=i+1;j<v.size()-1;j++)
        {
            sum=sum+bs(i,j);
        }
    }
    printf("%d",sum);
    return 0;
}