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 solveDP():int=
  var
    (n,m,a)=(scan(),scan(),scan())
    lrp = newseqwith(m,(scan(),scan(),scan()))
    le = newseqwith(n+2,newseq[int]())
    re = newseqwith(n+2,newseq[int]())
    dp = newseqwith(n+2,newseqwith(2,-int.high.div(4)))
  lrp = lrp.sorted()
  dp[1][1]=0
  for idx,(l,r,p) in lrp:
    le[l].add(idx)
    re[r].add(idx)
  for i in 1..n+1:
    #echo "i:", i
    if i>1:
      dp[i][0].max=max(dp[i-1][0],dp[i-1][1])
      dp[i][1].max=max(dp[i-1][0],dp[i-1][1])-a
    for idx in le[i]:
      #echo lrp[idx]
      if lrp[idx][1]==n:
        dp[lrp[idx][1]+1][1].max=max(lrp[idx][2]+dp[i][1],lrp[idx][2]+dp[i][0]-a)
      else:
        dp[lrp[idx][1]+1][1].max=max(lrp[idx][2]+dp[i][1],lrp[idx][2]+dp[i][0]-a)-a
    #echo dp.join("\n")
    #echo "###"
  return dp[n+1].max()




proc solve():int=
  var
    (n,m,a)=(scan(),scan(),scan())
    lrp = newseqwith(m,(scan()-1,scan()-1,scan()))
    le = newseqwith(n+1,newseq[int]())
    re = newseqwith(n+1,newseq[int]())
    memo = initTable[(int,int,),int]()
  lrp = lrp.sorted()
  for idx,(l,r,p) in lrp:
    le[l].add(idx)
    re[r].add(idx)

  # l-1とlのあいだ、rとr+1の間に黒線が存在するケース
  proc recSolve(l,r:int):int=
    echo l,", ", r
    if memo.hasKey((l,r)):
      return memo[(l,r)]
    for idx in le[l]:
      if lrp[idx][1]==r:
        result.max=lrp[idx][2]
    #
    for m in l..<r:
      result.max=(-a)+(recSolve(l,m)+recSolve(m+1,r))
    memo[(l,r)]=result
  return recSolve(0,n-1)

  
echo solveDP()