N, M, A = map(int, input().split())
G = [list() for _ in range(N+1)]
for i in range(M):
    l,r,p = map(int, input().split())
    l-=1
    G[r].append([l,p])
dp = [0]*(N+1)
res = 0
for i in range(1,N):
    for l, p in G[i]:
        dp[i] = max(dp[i],dp[l]+p-A)
    if dp[i]==0:
        dp[i] = -A
    res = max(res,dp[i])
for l, p in G[-1]:
    dp[-1] = max(dp[-1],dp[l]+p)
res = max(res,dp[-1])
print(res)