import sys
from operator import itemgetter


input = sys.stdin.readline
n, m, a = map(int, input().split())
info = [list(map(int, input().split())) for i in range(m)]

info = sorted(info, key = itemgetter(1))

dp = [0]*(n+1)
end = 0
max_dp = 0
for i in range(1, n + 1):
    if info[end][1] == i:
        while end < m and info[end][1] == i:
            if i == n:
                dp[i] = max(dp[i], max_dp, dp[info[end][0] - 1] + info[end][2])
            else:
                dp[i] = max(dp[i], max_dp - a, dp[info[end][0] - 1] + info[end][2] - a)
            end += 1
        max_dp = max(max_dp, dp[i])
    else:
        dp[i] = max_dp - a
print(max(dp))