#include <cstdio>
#include <algorithm>

using namespace std;

int v[810];
int mid;

int cauta_binar(int s,int st,int dr)
{
    while(st<=dr)
    {
        mid=(st+dr)/2;
        if(s<v[mid]) dr=mid-1;
        else st=mid+1;
    }
    return dr;
}

int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    int n,s=0;
    scanf("%d",&n);
    for(int i=1;i<=n;i++) scanf("%d",&v[i]);
    sort(v+1,v+n+1);
    for(int i=1;i<=n-1;i++)
        for(int j=i+1;j<=n;j++)
            s+=cauta_binar(v[i]+v[j],j,n)-j;
    printf("%d",s);
    return 0;
}