import sys
import pypyjit
import itertools
import heapq
import math
from collections import deque, defaultdict
import bisect

input = sys.stdin.readline
sys.setrecursionlimit(10 ** 6)
pypyjit.set_param('max_unroll_recursion=-1')


def index_lt(a, x):
    'return largest index s.t. A[i] < x or -1 if it does not exist'
    return bisect.bisect_left(a, x) - 1


def index_le(a, x):
    'return largest index s.t. A[i] <= x or -1 if it does not exist'
    return bisect.bisect_right(a, x) - 1


def index_gt(a, x):
    'return smallest index s.t. A[i] > x or len(a) if it does not exist'
    return bisect.bisect_right(a, x)


def index_ge(a, x):
    'return smallest index s.t. A[i] >= x or len(a) if it does not exist'
    return bisect.bisect_left(a, x)


N, M, A = map(int, input().split())
E = [[] for _ in range(N)]
for _ in range(M):
    l, r, p = map(int, input().split())
    l -= 1
    E[l].append((r, p))

INF = 1 << 50
dp = [-INF] * (N + 1)
dp[0] = 0
ma = 0
for i in range(N):
    for j, p in E[i]:
        if j == N:
            dp[j] = max(dp[j], dp[i] + p, ma + p - A)
        else:
            dp[j] = max(dp[j], dp[i] + p - A, ma + p - 2 * A)
    ma = max(ma, dp[i])
print(max(dp))