import collections

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

dp = [-float('inf')] * (n + 1)
dp[0] = 0
for last in range(0, n + 1):
    for nxt in range(last + 1, n):
        dp[nxt] = max(dp[nxt], dp[last] + d[(last, nxt)] - a)
    dp[n] = max(dp[n], dp[last] + d[(last, n)])

print(max(dp))