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])

DP=[0]*(N+2)
USE=[0]*(N+2)
USE[1]=1
USE[N+1]=1

for i in range(N+2):
    if DP[i-1]>=DP[i]:
        DP[i]=DP[i-1]
        USE[i]=0
    USE[1]=1
    
    for y,z in LLIST[i]:
        if USE[i]==1 and y==N+1:
            DP[y]=max(DP[y],DP[i]+z)

        elif USE[i]==0 and y==N+1:
            DP[y]=max(DP[y],DP[i]+z-A)

        elif USE[i]==1:
            DP[y]=max(DP[y],DP[i]+z-A)
            USE[y]=1

        elif USE[i]==0:
            DP[y]=max(DP[y],DP[i]+z-2*A)
            USE[y]=1

    #print(DP)

print(DP[-1])