#include <fstream>
#include <algorithm>

using namespace std;
int a[1000];

int caut( int st, int dr,int x ){
int save=0;
while ( st<= dr ) {
    int mid =( st+ dr)/2;
    if( x>= a[mid] )  st=mid+1; else dr=mid-1;
}
  return dr;
}

int main()
{
    ifstream in("nrtri.in");
    ofstream out("nrtri.out");

    int n; in>>n;
     for(int i=1; i<=n; i++)
        in>>a[i];
        sort(a+1,a+n+1);
 int sum=0;
    for ( int i=1; i<=n;  i++)
        for( int j=i+1; j<=n; j++){
            sum+= (caut(1,n,a[i]+a[j])-j);

    }

      out<<sum;


    return 0;
}