import sys
input = sys.stdin.readline

N,M,A=map(int,input().split())
L=[list(map(int,input().split())) for i in range(M)]

for i in range(M):
    L[i][1]+=1
    
LLIST=[[] for i in range(N+2)]

for x,y,z in L:
    LLIST[x].append([y,z])

USE=[-float("inf")]*(N+2)
NOUSE=[0]*(N+2)
USE[1]=0

for i in range(N+2):
    NOUSE[i]=max(USE[i-1],NOUSE[i-1])
    
    for y,z in LLIST[i]:
        if y==N+1:
            USE[y]=max(USE[y],USE[i]+z,NOUSE[i]+z-A)
            
        else:
            USE[y]=max(USE[y],USE[i]+z-A,NOUSE[i]+z-2*A)

    #print(DP)

print(max(USE[-1],NOUSE[-1]))