#include <iostream>
#include <string>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <vector>
#include <cmath>
#include <cstdlib>
#include <queue>
#include <stack>
#include <iomanip>


using namespace std;

#define REP(i, n) for(ll i = 0;i < n;i++)
#define REPR(i, n) for(ll i = n;i >= 0;i--)
#define FOR(i, m, n) for(ll i = m;i < n;i++)
#define FORR(i, m, n) for(ll i = m;i >= n;i--)
#define REPO(i, n) for(ll i = 1;i <= n;i++)
#define ll long long
#define INF (ll)1 << 60
#define MINF (-1 * INF)
#define ALL(n) n.begin(),n.end()
#define MOD (ll)1000000007
#define P pair<ll, ll>

ll n, m, a, dp[110000], dp2[110000], ans = MINF;
map<P, ll> mp;
vector<P> s;

//セグ木
ll dat[510000], sz;

void init(ll n) {
	sz = 1;
	while (sz < n)sz *= 2;
	REP(i, sz * 2 - 1) dat[i] = MINF; //初期値
}

void update(ll k, ll a) { //場所(0-indexed), 値
	k += sz - 1;
	dat[k] = a;
	while (k > 0) {
		k = (k - 1) / 2;
		dat[k] = max(dat[k * 2 + 1], dat[k * 2 + 2]); //更新
	}
}

ll query(ll a, ll b, ll k, ll l, ll r) { //[a, b) 呼ぶとき (a, b, 0, 0, sz)
	if (r <= a or b <= l)return MINF;
	if (a <= l and r <= b)return dat[k];
	ll v1 = query(a, b, k * 2 + 1, l, (l + r) / 2);
	ll v2 = query(a, b, k * 2 + 2, (l + r) / 2, r);
	return max(v1, v2); //戻り値
}

int main() {
	init(110000);
	REPO(i, 101010)dp[i] = MINF;
	update(0, 0);
	cin >> n >> m >> a;
	REP(i, m) {
		ll l, r, p;
		cin >> l >> r >> p;
		s.push_back(P(r, l));
		mp[P(r, l)] = p;
	}
	sort(ALL(s));
	REP(i, m) {
		ll l = s[i].second, r = s[i].first;
		ll now = dp[l - 1] + mp[P(r, l)] - a;
		if (l != 1) now = max(now, query(0, l - 1, 0, 0, sz) + mp[P(r, l)] - a * 2);
		//cout << now << " " << query(0, l - 1, 0, 0, sz) + mp[P(r, l)] << endl;
		if (r == n) now += a;
		dp[r] = max(dp[r], now);
		update(r, dp[r]);
	}
	REP(i, 110000) {
		ans = max(ans, dp[i]);
		//cout << dp[i] << " " << i << endl;
	}
	cout << ans << endl;
}