import sys

sys.setrecursionlimit(10**6)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.buffer.readline())
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def LI1(): return list(map(int1, sys.stdin.buffer.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def BI(): return sys.stdin.buffer.readline().rstrip()
def SI(): return sys.stdin.buffer.readline().rstrip().decode()
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = 10**16
# md = 998244353
md = 10**9+7

n,m,a=LI()
frm=[[] for _ in range(n+1)]
for _ in range(m):
    l,r,p=LI()
    l-=1
    frm[r].append((l,p-a))

dp=[0]*(n+1)
mx=0
for r in range(1,n+1):
    dp[r]=mx-a
    for l,p in frm[r]:
        dp[r]=max(dp[r],dp[l]+p)
    mx=max(mx,dp[r])
dp[-1]+=a

print(dp[-1])