let scan_int () = Scanf.scanf " %d" (fun x -> x)
let scan_array len read_func = Array.init len (fun _ -> read_func())
let print_int n = Printf.printf "%d\n" n

let rec binary_search left right array value =
  if right - left <= 1 then right
  else
    let mid = (left + right) / 2 in
    if array.(mid) < value then binary_search mid right array value
    else binary_search left mid array value
  

let () =
  let n = scan_int() in
  let l = scan_array n scan_int in
  let _ = Array.fast_sort compare l in
  let ans = ref 0 in
  let _ =
    for i = 0 to n-2 do
      for j = i+1 to n-1 do
        let sum = l.(i) + l.(j) in
        let k = binary_search j n l sum in
        ans := !ans + (k-j-1)
      done
    done in
  print_int !ans
