#include <cstdio>

using namespace std;

int a[802], n, i, j, k, sol, s;

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

    scanf("%d", &n);

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

    for(i=1;i<=n-2;i++)
    {
        for(j=i+1;j<=n-1;j++)
        {
            s=a[i]+a[j];
            k=j+1;

            while(k <= n && a[k] < s)
                sol++, k++;
        }
    }

    printf("%d", sol);

    return 0;
}