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)

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