import sys
input = lambda : sys.stdin.readline().rstrip()

write = lambda x: sys.stdout.write(x+"\n")
debug = lambda x: sys.stderr.write(x+"\n")
writef = lambda x: print("{:.12f}".format(x))


n,m,a = list(map(int, input().split()))
ns = [[(0,0)] for _ in range(n+1)]
for _ in range(m):
    l,r,p = list(map(int, input().split()))
    l -= 1
    ns[r].append((p,l))
dp = [0]*(n+1)
cum = 0
for i in range(1,n+1):
    val = cum
    for p,j in ns[i]:
        val = max(val, dp[j]+p)
    if i<n:
        val -= a
    dp[i] = val
    cum = max(cum, val)
ans = max(dp)
print(ans)