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

from operator import itemgetter

L.sort(key=itemgetter(1))
dp0 = [0]*(N+1)
dp1 = [0]*(N+1)
j = 0
for i in range(1, N+1):
    dp0[i] = max(dp0[i-1], dp1[i-1])
    dp1[i] = dp0[i]-A
    while j < M and L[j][1] == i:
        if L[j][0] == 1 and L[j][1] == N:
            dp1[i] = max(dp1[i], L[j][2])
        elif L[j][0] == 1:
            dp1[i] = max(dp1[i], L[j][2]-A)
        elif L[j][1] == N:
            dp1[i] = max(dp1[i], dp1[L[j][0]-1]+L[j][2], dp0[L[j][0]-1]+L[j][2]-A)
        else:
            dp1[i] = max(dp1[i], dp1[L[j][0]-1]+L[j][2]-A, dp0[L[j][0]-1]+L[j][2]-2*A)
        j += 1

print(max(max(dp0), max(dp1)))