#include <cstdio>
#include <algorithm>
using namespace std;
int a[810],n;
int bsearch(int st,int dr,int key,int key2){
 int j=-1,m;
  while(st<=dr){
   m = (st+dr)/2;
    if(a[m] > key+key2)
     dr=m-1;
     else
      {
          j=m;
          st=m+1;
      }
    }
  return j;
}
int main(){
    int i,j;
    long long num;
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    scanf("%d",&n);
    for(i=1;i<=n;i++)
     {scanf("%d",&a[i]);}
     sort(a+1,a+n+1);
     num=0;
    for (i=1; i<=n; i++)
        for (j=i+1; j<=n; j++)
            num+=bsearch(j,n,a[i],a[j])-j;

      printf("%d\n",num);
    return 0;
}