local mma = math.max
local mfl, mce, mmi = math.floor, math.ceil, math.min

local n = io.read("*n")

local x, y = {}, {}
for i = 1, n do
  x[i], y[i] = io.read("*n", "*n")
end
if n == 1 then print(0) os.exit() end

local function lensq(i, j)
  return (1LL * x[i] - x[j]) * (1LL * x[i] - x[j]) + (1LL * y[i] - y[j]) * (1LL * y[i] - y[j])
end
local e1, e2 = {}, {}
local v = {}
local alive = {}
for i = 1, n do alive[i] = true end

local c = 0

local idxes = {}

for i = 1, n - 1 do
  for j = i + 1, n do
    c = c + 1
    e1[c], e2[c] = i, j
    v[c] = lensq(i, j)
    idxes[c] = c
  end
end
table.sort(idxes, function(a, b) return v[a] < v[b] end)
local ret = 0
for i = 1, c do
  local idx = idxes[i]
  local z1, z2 = e1[idx], e2[idx]
  if z1 == 1 then
    if alive[z2] then
      ret = ret + 1
      alive[z2] = false
    end
  else
    if alive[z1] and alive[z2] then
      alive[z1], alive[z2] = false, false
    end
  end
end
print(ret)