local n, m, a = io.read("*n", "*n", "*n")
local t = {}
for i = 1, m do
  t[i] = {}
  t[i].l, t[i].r, t[i].p = io.read("*n", "*n", "*n")
end
table.sort(t, function(x, y)
  if x.r ~= y.r then
    return x.r < y.r
  else
    return x.l < y.l
  end
end)

local mma = math.max
local ret = {}
local inf = -100000000000000
for i = 1, n do ret[i] = inf end
for i = 1, m do
  local l, r, p = t[i].l, t[i].r, t[i].p
  local cost = r == n and 0 or a
  if l == 1 then
    ret[r] = mma(ret[r], p - cost)
  else
    if ret[l - 1] == inf then
      ret[l - 1] = -a
    end
    ret[r] = mma(ret[r], ret[l - 1] + p - cost)
  end
end
local tot = 0
for i = 1, n do
  tot = mma(tot, ret[i])
end
print(tot)