n,m,a=map(int,input().split())
x=[[] for i in range(n)]
dp=[-1<<60]*(n+1)
dp[0]=0
for i in range(m):
    l,r,p=map(int,input().split())
    x[l-1].append((r,p))
ans=0;f=0
for i in range(n):
    for j,l in x[i]:
        dp[j]=max(dp[j],dp[i]+l-a,f-a*2+l)
    f=max(f,dp[i])
    ans=max(ans,dp[i])
print(max(ans,dp[n]+a))