import sys
input = sys.stdin.buffer.readline
sys.setrecursionlimit(10 ** 7)

N, M, A = map(int, input().split())
LRX = list(tuple(map(int, input().split())) for _ in range(M))
LRX.sort(key=lambda x: x[1])

p = 0
dp = [0] * (N + 1)
for i in range(1, N):
    while p < M and LRX[p][1] == i:
        l, r, x = LRX[p]
        p += 1
        dp[r] = max(dp[r], dp[l - 1] + x - A)
while p < M:
    l, r, x = LRX[p]
    p += 1
    dp[r] = max(dp[r], dp[l - 1] + x)

print(max(dp))