#include <cstdio>
#include <algorithm>

using namespace std;
int v[805], n;

int cautare(int a, int b)
{
    int l, r, med, val;
    l=b+1;
    r=n;
    val=v[a]+v[b];
    while(l<=r)
    {
        med=(l+r)/2;
        if (val<v[med])
            r=med-1;
        else
            l=med+1;
    }
    return r-b;
}

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