from operator import itemgetter
import sys
class Segtree:
    def __init__(self, A, intv, initialize = True, segf = min):
        self.N = len(A)
        self.N0 = 2**(self.N-1).bit_length()
        self.intv = intv
        self.segf = segf
        if initialize:
            self.data = [intv]*(self.N0-1) + A + [intv]*(self.N0 - self.N + 1)
            for i in range(self.N0-2, -1, -1):
                self.data[i] = self.segf(self.data[2*i+1], self.data[2*i+2]) 
        else:
            self.data = [intv]*(2*self.N0)
        
    def update(self, k, x):
        k += self.N0-1
        self.data[k] = x
        while k >= 0 :
            k = (k-1)//2
            self.data[k] = self.segf(self.data[2*k+1], self.data[2*k+2])
    
    def query(self, l, r):
        L, R = l+self.N0, r+self.N0
        s = self.intv
        while L < R:
            if R & 1:
                R -= 1
                s = self.segf(s, self.data[R-1])
            if L & 1:
                s = self.segf(s, self.data[L-1])
                L += 1
            L >>= 1
            R >>= 1
        return s

            

N, M, A = map(int, input().split())
LRP = [tuple(map(int, sys.stdin.readline().split())) for _ in range(M)]

Edge = [[] for _ in range(N+1)]
for l, r, p in LRP:
    Edge[r].append((l, p))

Dp = [0]*(N+1)
dp = Segtree([0]*(N+1), 0, False, max)

for i in range(1, N+1):
    res = -A
    res = max(dp.query(0, i) - A, res)
    for l, c in Edge[i]:
        res = max(res, Dp[l-1] + c - A)
    Dp[i] = res
    dp.update(i, res)
Dp[-1] += A
print(max(Dp))