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