#region Header
#!/usr/bin/env python3
# from typing import *

import sys
import io
import math
import collections
import decimal
import itertools
from queue import PriorityQueue
import bisect
import heapq

def input():
    return sys.stdin.readline()[:-1]

sys.setrecursionlimit(1000000)
#endregion

# _INPUT = """5 2 1
# 1 1 2
# 2 5 10
# """
# sys.stdin = io.StringIO(_INPUT)


def main():
    N, M, A = map(int, input().split())

    points = dict()
    T1 = [list() for _ in range(N+1)]
    T2 = [list() for _ in range(N+1)]
    for _ in range(M):
        l, r, p = map(int, input().split())
        l -= 1
        points[(l, r)] = p
        T1[l].append(r)
        T2[r].append(l)

    dp = [0 for _ in range(N+1)]
    for i in range(1, N+1):

        v_max = -10**10
        for j in range(i):
            v = dp[j]
            if (j, i) in points:
                v += points[(j, i)]
            if i < N:
                v -= A
            v_max = max(v_max, v)
        dp[i] = v_max

    print(dp[N])

if __name__ == '__main__':
    main()