#include<cstdio>
#include<algorithm>
using namespace std;
int n,nr,val,a[805];
int cb(int x, int st, int dr)
{
    int mij;
    while (st<=dr)
        {
            mij=(st+dr)/2;
            if (a[mij]<x) st=mij+1;
            else dr=mij-1;
        }
    return dr+1;
}
int main()
{
    int i,j;
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    scanf("%d",&n);
    for (i=1;i<=n;++i)
        scanf("%d",&a[i]);
    sort(a+1,a+n+1);
    for (i=1;i<n-1;++i)
        for (j=i+2;j<=n;++j)
            {
                val=cb(a[j]-a[i],i+1,j-1);
                nr+=(j-val);
            }
    printf("%d\n",nr);
    return 0;
}