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

def f(current):
    ans = d[(current, n)] # 線を引かない場合
    for nxt in range(current + 1, n):
        ans = max(ans, f(nxt) + d[(current, nxt)] - a)
    return ans

print(f(0))