#include<stdio.h>
#include<algorithm>
using namespace std;
int v[1001];
int find(int a,int b,int x){
    int l1=a,l2=b,m,elem;
    while(l1<=l2){
        m=(l1+l2)/2;
        if(v[m]<=x){
            elem=m;
            l1=m+1;
        }
        else
            l2=m-1;
    }
    return elem;
}
int main() {
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    int n,i,j,a,b,nr=0;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
        scanf("%d",&v[i]);
    sort(v+1,v+n+1);
    for(i=1;i<=n-2;i++)
        for(j=i+1;j<=n-1;j++)
            nr=nr+find(j+1,n,v[i]+v[j])-j;
    printf("%d",nr);
    return 0;
}