//Hash?: O(n^2)
#include <stdio.h>
#include <algorithm>

#define NM 802

using namespace std;

int a[NM];
int h[60003];
long long sol;
int okpos;
int n;

int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);

    int i, j;
    scanf("%d", &n);

    for (i=1; i<=n; ++i)
	scanf("%d", &a[i]);

    sort(a+1, a+n+1);
    j=0;
    for (i=1; i<=a[n-1]+a[n]; ++i)
    {
	while (j<=n && a[j]<=i) ++j; --j; 
	h[i]=j;
    } 
    
    for (i=1; i<n-1; ++i)
	for (j=i+1; j<n; ++j) 
	    if (h[a[i]+a[j]]>j) sol+=h[a[i]+a[j]]-j; 

    printf("%lld", sol);

    fclose(stdin);
    fclose(stdout);

    return 0;
}