#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
#include <tuple>
#include <assert.h>
#include <deque>
#include <bitset>
#include <iomanip>
#include <limits>
#include <chrono>
#include <random>
#include <array>
#include <unordered_map>
#include <functional>
#include <complex>
#include <numeric>

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

constexpr long long MAX = 5100000;
constexpr long long INF = 1LL << 60;
constexpr int inf = 1 << 28;
constexpr long long mod = 1000000007LL;
//constexpr long long mod = 998244353LL;

using namespace std;
typedef unsigned long long ull;
typedef long long ll;


int main()
{
	/*
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	*/

	ll n, m, A; scanf("%lld %lld %lld", &n, &m, &A);
	vector<vector<pair<int, ll>>> g(n);
	for (int i = 0; i < m; i++) {
		ll l, r, p; scanf("%lld %lld %lld", &l, &r, &p);
		l--; r--;
		g[r].emplace_back(l, p);
	}
	vector<ll> dp(n + 1, -INF);
	dp[0] = 0;
	ll mx = 0;
	for (int i = 0; i < n; i++) {
		ll cost = -A;
		if (i == n - 1) cost = 0;
		ll tmp = cost;
		for (auto left : g[i]) {
			if (left.first == 0) chmax(tmp, left.second + cost);
			else chmax(tmp, dp[left.first - 1] + left.second + cost);
		}
		chmax(tmp, mx + cost);
		dp[i] = tmp;
		chmax(mx, tmp);
	}
	cout << *max_element(dp.begin(), dp.end()) << endl;
    return 0;
}