import times, strutils, sequtils, math, algorithm, tables, sets, lists, intsets
import critbits, future, strformat, deques
template `max=`(x,y) = x = max(x,y)
template `min=`(x,y) = x = min(x,y)
template `mod=`(x,y) = x = x mod y
template scan2 = (scan(), scan())
template scan3 = (scan(), scan())
let read* = iterator: string {.closure.} =
    while true: (for s in stdin.readLine.split: yield s)
proc scan(): int = read().parseInt
proc scanf(): float = read().parseFloat
proc toInt(c:char): int =
    return int(c) - int('0')



proc solve():int=
  var
    (n,m,a)=(scan(),scan(),scan())
    lrp = newseqwith(m,(scan()-1,scan(),scan()))
    dp = newseqwith(n+1,newseqwith(2,0))
    es = newseqwith(n+1,newseq[int]())
    ps = newseqwith(n+1,newseq[int]())
  for (l,r,p) in lrp:
    es[r].add(l)
    ps[r].add(p)
  # 右端から左端をたどれるようにする
  #echo es
  #echo ps
  for r in 1..n:
    dp[r][0].max=max(dp[r-1])
    dp[r][1] = dp[r][0]-a
    for lIdx in 0..<es[r].len:
      var
        l = es[r][lIdx]
        p = ps[r][lIdx]
      if l == 0 and r == n:
        dp[r][1].max=dp[l][1]+p
      elif l == 0:
        dp[r][1].max=dp[l][1]-a+p
      elif r == n:
        dp[r][1].max=dp[l][0]-a+p
        dp[r][1].max=dp[l][1]+p
      else:
        dp[r][1].max=dp[l][0]-a-a+p
        dp[r][1].max=dp[l][1]-a+p
  #echo dp.join("\n")
  return dp[^1].max()

  
echo solve()