from operator import itemgetter

def update(i, x):
    while i < n + 1:
        if x > bit[i]:
            bit[i] = x
        i += i & -i

def get(i):
    mx = 0
    while i > 0:
        if mx < bit[i]:
            mx = bit[i]
        i -= i & -i
    return mx

n, m, a = map(int, input().split())
ku = [list(map(int, input().split())) for _ in range(m)]
ku.sort(key=itemgetter(1))
bit = [0] * (n + 1)
dp = [-a] * (n + 1)
for l, r, p in ku:
    if l - 1:
        dp[r] = max(dp[l - 1] + p - a, get(l - 1) + p - 2 * a, dp[r])
        update(r, dp[r])
    else:
        dp[r] = max(p - a, dp[r])
        update(r, dp[r])
update(n,dp[n]+a)
print(get(n))