#!/usr/bin/env python3
# %%
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines


# %%
N, M, A = map(int, readline().split())
m = map(int, read().split())
LRP = zip(m, m, m)

# %%
intervals = [[] for _ in range(N + 1)]
for l, r, p in LRP:
    intervals[r].append((l, p))


# %%
dp = [0] + [-A] * N
dp_cummax = [0] * (N + 1)

for r in range(1, N + 1):
    for l, p in intervals[r]:
        x = dp[l - 1] + p - A
        if dp[r] < x:
            dp[r] = x
        if l > 1:
            x = dp_cummax[l - 2] + p - 2 * A
            if dp[r] < x:
                dp[r] = x
    dp_cummax[r] = max(dp_cummax[r - 1], dp[r])

dp[N] += A

# %%
print(max(dp))