#include<stdio.h>
#include<algorithm>
using namespace std;
int s;
int main()
{
    int n,i,v[805],j;
    freopen("nrtri.in","r",stdin);
    scanf("%d",&n);for(i=1;i<=n;++i) scanf("%d",&v[i]);
    fclose(stdin);
    sort(v+1,v+1+n);
    for(i=n;i>2;--i)
    {
        int a=v[i]-v[i-1];
        for(j=1;j<=n && v[j]<a;j++);
        s+=i-1-j;
    }
    freopen("nrtri.out","w",stdout);printf("%d",s);
    fclose(stdout);
    return 0;
}