import collections

n, m, a = map(int, input().split())
edge = collections.defaultdict(list)
for _ in range(m):
    l, r, p = map(int, input().split())
    edge[l - 1].append((r, p))

dp = [-a] * (n + 1)
dp[0] = 0
for last in range(0, n + 1):
    for nxt, score in edge[last]:
        if nxt == n:
            dp[nxt] = max(dp[nxt], dp[last] + score)
        else:
            dp[nxt] = max(dp[nxt], dp[last] + score - a)

print(max(dp))