#include<fstream>
#include<algorithm>
using namespace std;
ifstream cin("nrtri.in");
ofstream cout("nrtri.out");
short a[800];
int b[30001];
int main()
{
    int i=0,j=0,k=0,n;
    for(cin>>n;i<n;cin>>a[i++]);
    for(sort(a,a+n),i=a[0]+1;i<=a[n-1]-a[1];b[i++]=j)
        for(;a[j]<i;++j);
    for(i=1;i<n-1;++i)
        for(j=i+1;j<n&&a[j]<=2*a[i];k+=i-b[a[j++]-a[i]]);
    return cout<<k,0;
}