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