class SegTree:
    def __init__(self, init_val, ide_ele, segfunc):
        self.n = len(init_val)
        self.num = 2**(self.n-1).bit_length()
        self.ide_ele = ide_ele
        self.segfunc = segfunc
        self.seg = [ide_ele]*2*self.num
        # set_val
        for i in range(self.n):
            self.seg[i+self.num] = init_val[i]
        # built
        for i in range(self.num-1, 0, -1):
            self.seg[i] = self.segfunc(self.seg[2*i], self.seg[2*i+1])

    def update(self, k, x):
        k += self.num
        self.seg[k] = x
        while k:
            k = k >> 1
            self.seg[k] = self.segfunc(self.seg[2*k], self.seg[2*k+1])

    def query(self, l, r):
        if r <= l:
            return self.ide_ele
        l += self.num
        r += self.num
        lres = self.ide_ele
        rres = self.ide_ele
        while l < r:
            if r & 1:
                r -= 1
                rres = self.segfunc(self.seg[r], rres)
            if l & 1:
                lres = self.segfunc(lres, self.seg[l])
                l += 1
            l = l >> 1
            r = r >> 1
        res = self.segfunc(lres, rres)
        return res

    def __str__(self): # for debug
        arr = [self.query(i,i+1) for i in range(self.n)]
        return str(arr)

import sys
import io, os
input = io.BytesIO(os.read(0,os.fstat(0).st_size)).readline

INF = 10**18

def main():
    n, m, a = map(int, input().split())
    L = [0]*n
    R = [[] for i in range(n)]
    for i in range(m):
        l, r, p = map(int, input().split())
        l, r = l-1, r-1
        R[r].append((l, p))

    seg = SegTree([-INF]*(n+2), -INF, max)
    seg.update(0, 0)
    for i in range(n):
        for l, p in R[i]:
            t = max(seg.query(0, l)-a, seg.query(l, l+1))
            if i != n-1:
                seg.update(i+1, max(seg.query(i+1, i+2), t+p-a))
            else:
                seg.update(i+1, max(seg.query(i+1, i+2), t+p))
    #print(seg)
    print(seg.query(0, n+1))

if __name__ == '__main__':
    main()