import sys; input = sys.stdin.buffer.readline
sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

class SegmentTree(object):
	#N:処理する区間の長さ
	def __init__(self, N):
		self.N0 = 2 ** (N - 1).bit_length()
		self.data = [-INF] * (2 * self.N0)

	#k番目の値をxに更新
	def update(self, k, x):
		k += self.N0 - 1
		self.data[k] = x
		while k > 0:
			k = (k - 1) // 2
			self.data[k] = max(self.data[2 * k + 1], self.data[2 * k + 2])

	#区間[l, r]の最大値
	def query(self, l, r):
		L = l + self.N0; R = r + self.N0 + 1
		m = -INF
		while L < R:
			if R & 1:
				R -= 1
				m = max(m, self.data[R - 1])
			if L & 1:
				m = max(m, self.data[L - 1])
				L += 1
			L >>= 1; R >>= 1

		return m

#処理内容
def main():
	N, M, A = getlist()
	line = []
	for i in range(M):
		l, r, p = getlist()
		line.append([r, l, p])
	line.sort()
	
	# セグ木でDP
	Seg = SegmentTree(N + 2)
	Seg.update(0, 0)
	for i in range(M):
		r, l, p = line[i]
		if r != N:
			newScore = max(Seg.query(0, l - 1) - 2 * A + p, Seg.query(l - 1, l - 1) - A + p, Seg.query(r, r))
		else:
			newScore = max(Seg.query(0, l - 1) - A + p, Seg.query(l - 1, l - 1) + p, Seg.query(r, r))
		Seg.update(r, newScore)

	ans = max(Seg.data)
	print(ans)

if __name__ == '__main__':
	main()