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

dp = [-10 ** 9 - 5] * (N + 1)
dp[0] = 0
cur_max = 0
for i, s in enumerate(sections):
    dp[i] = max(dp[i], cur_max - A)
    cur = dp[i]
    for r, p in s:
        dp[r] = max(dp[r], cur + p - (A if r != N else 0))
    cur_max = max(cur_max, cur)

print(max(dp))