# coding: utf-8
# Your code here!

n,m,a = [int(i) for i in input().split()]
lrp = [[int(i) for i in input().split()] for _ in range(m)] + [[1,i,0] for i in range(1,n+1)] + [[i,n,0] for i in range(1,n+1)]


lrp.sort(key = lambda x: x[1])

inf = 1e18
dp = [-inf]*(n+1)
dp[0] = 0

for l,r,p in lrp:
    l-=1
    r-=1
    if r != n-1:
        dp[r+1] = max(dp[r+1], dp[l]+p-a)
    else:
        dp[r+1] = max(dp[r+1], dp[l]+p)
        
#print(dp)

print(max(dp))