N,M,a = map(int,input().split())
D = [[] for _ in range(N+1)]
for _ in range(M):
    l,r,p = map(int,input().split())
    D[r].append((l,p))
dp = [0]*(N+1)
for i in range(1,N+1):
    dp[i] = dp[i-1]
    if len(D[i])>0:
        for l,p in D[i]:
            if l==1 or dp[l-1]>dp[l-2]:
                if i<N and p>a:
                    dp[i] = max(dp[i],dp[l-1]+p-a)
                elif i==N:
                    dp[i] = max(dp[i],dp[l-1]+p)
            else:
                if i<N and p>2*a:
                    dp[i] = max(dp[i],dp[l-1]+p-2*a)
                elif i==N and p>a:
                    dp[i] = max(dp[i],dp[l-1]+p-a)
print(dp[N])