#include <stdio.h>
#include <algorithm>
using namespace std;

int v[801], n;

int caut(int val)
{
    int i, step;
    for (step = 1; step <n; step <<= 1);
    for (i = 0; step; step >>= 1){
        if (i + step <= n && v[i + step] <= val){
           
		}
	}
    return i;
}

int main ()
{
    freopen("nrtri.in", "r", stdin);
    freopen("nrtri.out", "w", stdout);
    int i, j, c=0, x;
    scanf("%d", &n);
    for (i=1; i<=n; i++)
        scanf ("%d", &v[i]);
    sort(v+1, v+n+1);
    for (i=1; i<=n-2; i++) {
        for (j=i+1; j<=n-1; j++) {
            x=(caut(v[i]+v[j])-j);
            c+=x;
        }
    }
    printf("%d", c);
    return 0;
}