#include<bits/stdc++.h>
using namespace std;
#define FOR(i,s,t) for(int i = s; i < t; i++)
using LL = long long;
using VL = vector<LL>;

int main() {

	int N, M, A; cin >> N >> M >> A;
	using PII = pair<int, int>;
	vector<vector<PII>>seg(N + 1);
	FOR(i, 0, M) {
		int L, R, V; cin >> L >> R >> V;
		seg[R].emplace_back(L, V);
	}
	const int USED = 1;
	const int SETED = 0;
	const LL LINF = 1e18;
	vector<VL> dp(N + 1, VL(2, -LINF));
	auto setmax = [](LL &a, LL b) {a = max(a, b); };
	dp[0][SETED] = 0;
	LL allmax = 0;
	FOR(R, 1, N + 1) {
		for (auto it : seg[R]) {
			int L = it.first; LL v = it.second + (R == N ? 0 : -A);
			setmax(dp[R][USED], dp[L - 1][SETED] + v);
		}
		setmax(dp[R][SETED], allmax - A);
		setmax(dp[R][SETED], dp[R][USED]);

		setmax(allmax, dp[R][SETED]);
		setmax(allmax, dp[R][USED]);
	}

	LL ans = 0;
	FOR(i, 0, N + 1) {
		setmax(ans, dp[i][USED]);
		setmax(ans, dp[i][SETED]);
	}
	cout << ans << endl;
}