import sys
readline = sys.stdin.readline

N, M, A = map(int, readline().split())
D = [[] for i in range(N + 1)]
for i in range(M):
    L, R, P = map(int, readline().split())
    if R == N:
        P += A
    D[L - 1].append((R, P - 2 * A))

inf = 10 ** 18
dp = [[-inf] * 2 for i in range(N + 1)]
dp[0][1] = 0
for i in range(N):
    dp[i + 1][0] = max(dp[i + 1][0], dp[i][0], dp[i][1])
    for R, C in D[i]:
        dp[R][1] = max(dp[R][1], dp[i][1] + C + A)
        dp[R][1] = max(dp[R][1], dp[i][0] + C)

ans = 0
for i in range(N + 1):
    ans = max(ans, max(dp[i]))
print(ans)