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

LLIST=[[] for i in range(N+2)]

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

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

for i in range(N+2):
    DP[i]=DP[i-1]
    
    for x,z in LLIST[i]:
        if i==x and USE[i]==1:
            DP[i]=DP[i]+z
            
        elif i==x and USE[i]==0:
            if DP[i]<DP[i]+z-A:
                DP[i]=DP[i]+z-A
                USE[i]=1
            
        elif i==N+1 and USE[x]==1:
            if DP[i]<DP[x]+z:
                DP[i]=DP[x]+z

        elif i==N+1 and USE[x]==0:
            if DP[i]<DP[x]+z-A:
                DP[i]=DP[x]+z-A

        elif USE[x]==1:
            if DP[i]<DP[x]+z-A:
                DP[i]=DP[x]+z-A
                USE[i]=1
                
        elif USE[x]==0:
            if DP[i]<DP[x]+z-2*A:
                DP[i]=DP[x]+z-2*A
                USE[i]=1


print(DP[-1])