n,m,a = map(int,input().split())
lrp = [[int(i)-1 for i in input().split()] for j in range(m)]

lrp.sort()
dp = [[-10**15]*2 for i in range(n+1)]
dp[0][1] = 0
dp[n][1] = 0
for i in range(n):
    dp[i][0] = 0

for i in range(m):
    l,r,p = lrp[i]
    p += 1
    r += 1
    if l != 0:
        if r != n:
            dp[r][1] = max(0,dp[l][1]+p-a,dp[l][0]+p-2*a,dp[r][1])
        else:
            dp[r][1] = max(0,dp[l][1]+p,dp[l][0]+p-a,dp[r][1])
    else:
        if r != n:
            dp[r][1] = max(0,dp[l][1]+p-a,dp[l][0]+p-a,dp[r][1])
        else:
            dp[r][1] = max(0,dp[l][1]+p,dp[l][0]+p,dp[r][1])

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

print(ans)