#include <bits/stdc++.h>

int main()
{
	int N, M, A;
	scanf("%d%d%d", &N, &M, &A);
	using vpi = std::vector<std::pair<int, int64_t>>;
	using vvpi = std::vector<vpi>;

	vvpi spans(N + 1);
	for (int i{}; i < M; i++)
	{
		int l, r;
		int64_t p;
		scanf("%d%d%lld", &l, &r, &p);
		spans[r].push_back({l, p});
	}
	std::vector<int64_t> dp(N + 1, -(1ll << 60));
	std::vector<int64_t> maxDP(N + 1);
	dp[0] = 0;
	for (int i{1}; i <= N; i++)
	{
		for (auto& e: spans[i])
		{
			int64_t last_bonus{};
			if (i == N) last_bonus += A;
			if (dp[e.first - 1] != -(1ll << 60))
				dp[i] = std::max(dp[i], dp[e.first - 1] + e.second - A + last_bonus);
				
			if (e.first > 1)
				dp[i] = std::max(dp[i], maxDP[e.first - 2] + e.second - 2 * A + last_bonus);
		}
		maxDP[i] = std::max({maxDP[i - 1], dp[i]});
	}
	printf("%lld\n", maxDP.back());

	return 0;
}