#include<cstdio>
#include<algorithm>
using namespace std;
int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    int n,i,j,k,l[1001],q=0;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
        scanf("%d",&l[i]);
    sort(l+1,l+n+1);
    for(i=1;i<=n-2;i++)
        for(j=i+2;j<=n&&l[i]+l[j]>=l[k];j++)
                q++;
    printf("%d\n",q);
    return 0;
}