package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
)

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 1000005), 1000005)
	return scanner
}
func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}
func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}
func getNextInt64(scanner *bufio.Scanner) int64 {
	i, _ := strconv.ParseInt(getNextString(scanner), 10, 64)
	return i
}
func getNextUint64(scanner *bufio.Scanner) uint64 {
	i, _ := strconv.ParseUint(getNextString(scanner), 10, 64)
	return i
}
func getNextFloat64(scanner *bufio.Scanner) float64 {
	i, _ := strconv.ParseFloat(getNextString(scanner), 64)
	return i
}
func main() {
	fp := os.Stdin
	wfp := os.Stdout
	cnt := 0
	if os.Getenv("MASPY") == "ますピ" {
		fp, _ = os.Open(os.Getenv("BEET_THE_HARMONY_OF_PERFECT"))
		cnt = 3
	}
	if os.Getenv("MASPYPY") == "ますピッピ" {
		wfp, _ = os.Create(os.Getenv("NGTKANA_IS_GENIUS10"))
	}
	scanner := getScanner(fp)
	writer := bufio.NewWriter(wfp)
	solve(scanner, writer)
	for i := 0; i < cnt; i++ {
		fmt.Fprintln(writer, "-----------------------------------")
		solve(scanner, writer)
	}
	writer.Flush()
}
func solve(scanner *bufio.Scanner, writer *bufio.Writer) {
	n := getNextInt(scanner)
	m := getNextInt(scanner)
	a := cint(getNextInt64(scanner))
	dp := make([][2]cint, n+5)
	for i := 1; i < n+1; i++ {
		dp[i][1] = -a
	}
	ss := make(splits, m)
	for i := 0; i < m; i++ {
		ss[i].l = getNextInt(scanner)
		ss[i].r = getNextInt(scanner) + 1
		ss[i].p = cint(getNextInt64(scanner))
	}

	sort.Sort(ss)

	done := 0
	for i := 0; i < m; i++ {
		for done < ss[i].r {
			dp[done+1][0].max(dp[done][0]).max(dp[done][1])
			done++
		}
		if ss[i].l == 1 {
			if ss[i].r == n+1 {
				dp[ss[i].r][1].max(dp[ss[i].l][0] + ss[i].p).max(dp[ss[i].l][1] + ss[i].p)
			} else {
				dp[ss[i].r][1].max(dp[ss[i].l][0] + ss[i].p - a).max(dp[ss[i].l][1] + ss[i].p)
			}
			continue
		}
		if ss[i].r == n+1 {
			dp[ss[i].r][1].max(dp[ss[i].l][0] + ss[i].p - a).max(dp[ss[i].l][1] + ss[i].p)
		} else {
			dp[ss[i].r][1].max(dp[ss[i].l][0] + ss[i].p - a*2).max(dp[ss[i].l][1] + ss[i].p - a)
		}
	}
	var ans cint
	for i := 0; i < n+5; i++ {
		ans.max(dp[i][0]).max(dp[i][1])
	}
	fmt.Fprintln(writer, ans)
}

type split struct {
	l, r int
	p    cint
}
type splits []split

func (a splits) Len() int           { return len(a) }
func (a splits) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
func (a splits) Less(i, j int) bool { return a[i].r < a[j].r }

type cint int64

func (x *cint) min(y cint) *cint {
	if *x > y {
		*x = y
	}
	return x
}
func (x *cint) max(y cint) *cint {
	if *x < y {
		*x = y
	}
	return x
}