local mfl = math.floor

local function comp(a, b)
  return a < b
end

local function lower_bound(ary, x)
  local num = #ary
  if num == 0 then return 1 end
  if not comp(ary[1], x) then return 1 end
  if comp(ary[num], x) then return num + 1 end
  local min, max = 1, num
  while 1 < max - min do
    local mid = mfl((min + max) / 2)
    if comp(ary[mid], x) then
      min = mid
    else
      max = mid
    end
  end
  return max
end

local n = io.read("*n")
local t = {}
for i = 1, n do
  t[i] = io.read("*n")
end
table.sort(t)
local ret = 0
for i = 1, n - 2 do
  for j = i + 1, n - 1 do
    local lb = lower_bound(t, t[i] + t[j]) - 1
    ret = ret + lb - j
  end
end
print(ret)