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
local curmax = {}
local curpos = 1
for i = 1, n do curmax[i] = 0 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
    -- print(i, l, r, p, ret[l - 1])
    if ret[l - 1] == inf then
      -- ret[r] = mma(ret[r], -a + p - cost)
      ret[l - 1] = curmax[l - 1] - a
    end
    ret[r] = mma(ret[r], ret[l - 1] + p - cost)
  end
  if curpos ~= r then
    for k = curpos + 1, r do
      curmax[k] = mma(curmax[k], curmax[k - 1])
    end
    curpos = r
  end
  curmax[r] = mma(curmax[r], ret[r])
end
local tot = 0
for i = 1, n do
  -- print(i, ret[i])
  tot = mma(tot, ret[i])
end
print(tot)