#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,x,i;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&x);
        v.push_back(x);
    }
    sort(v.begin(),v.end());
    int nr=0;
    vector<int>::iterator it1,it2,it3;
    for(it1=v.begin()+2;it1!=v.end();it1++)
    {
        for(it2=v.begin();it2!=it1;it2++)
        {
            it3=lower_bound(it2+1,it1,((*it1)-(*it2)));
            nr+=(int)(it1-it3);
        }
    }
    printf("%d",nr);
    return 0;
}