n,m,a = map(int,input().split())
query = [[] for i in range(n+5)]
for _ in range(m):
    l,r,p = map(int,input().split())
    query[r].append([l,p])

dp = [0]*(n+5)
ans = 0
for i in range(1,n+1):
    dp[i] = ans-a
    for l,p in query[i]:
        num = dp[l-1]+p
        if i != n:
            num -= a
        dp[i] = max(dp[i],num)
    ans = max(ans,dp[i])
print(ans)