local mfl = math.floor
local mce = math.ceil
local function comp(a, b)
  return a[1] < 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, d, a = io.read("*n", "*n", "*n")
d = d * 2
local t = {}
local imos = {}
for i = 1, n do
  t[i] = {io.read("*n", "*n")}
  imos[i] = 0
end
imos[n + 1] = 0
table.sort(t, function(a, b) return a[1] < b[1] end)
local ret = 0
for i = 1, n do
  local x, h = t[i][1], t[i][2]
  if 1 < i then
    imos[i] = imos[i] + imos[i - 1]
  end
  h = h + imos[i]
  if 0 < h then
    local use = mce(h / a)
    ret = ret + use
    local dst = lower_bound(t, x + d + 1)
    imos[i + 1] = imos[i + 1] - use * a
    imos[dst] = imos[dst] + use * a
  end
end
print(ret)
