#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

vector<int>v;

int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    int n,i,x,j,s,poz;
    vector<int>::iterator ind;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&x);
        v.push_back(x);
    }
    sort(v.begin(),v.end());
    s=0;
    for(i=0;i<v.size()-3;i++)
        for(j=i+1;j<v.size()-2;j++)
            {
                ind=upper_bound(v.begin(),v.end(),v[i]+v[j]);
                poz=(int)(ind-v.begin()-j);
                s=s+poz;
            }
    printf("%d",s);
    return 0;
}