#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+1;j<=n-1;j++)
			for (k=j+1;k<=n&&l[i]+l[j]>=l[k];k++)
					q++;
    printf("%d\n",q);
    return 0;
}