#include <stdio.h>
#include <algorithm>

using namespace std;

int main(){
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    
    long n,i,j,k,q=0,a[1024],x,next[32768];
    
    scanf("%ld",&n);
    for (i=1;i<=n;i++)
        scanf("%ld",&a[i]);
    sort(a+1,a+n+1);
    for (i=1;i<n;i++)
        for (j=a[i];j<a[i+1];j++)next[j]=i;
    next[a[n]]=n;
    for (i=1;i<=n-2;i++)
        for (j=i+1;j<=n-1;j++)
            q+=next[a[i]+a[j]]-j;
    
    printf("%ld\n",q);
return 0;
}