#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>

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; }

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

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

vector<pair<int, ll>> g[100010];
int main()
{
	/*
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	*/
	ll N, M, A; scanf("%lld %lld %lld", &N, &M, &A);
	for (int i = 0; i < M; i++) {
		ll l, r, p; scanf("%lld %lld %lld", &l, &r, &p);
		g[r].emplace_back(l, p);
	}
	vector<ll> dp(N + 5);
	dp[0] = 0;
	ll res = 0;
	ll mx = 0;
	for (ll i = 1; i <= N; i++) {
		for (auto e : g[i]) {
			chmax(dp[i], dp[e.first - 1] + e.second);
		}
		chmax(dp[i], mx);
		if(i != N) dp[i] -= A;
		chmax(mx, dp[i]);
		chmax(res, dp[i]);
	}
	cout << res << endl;
	return 0;
	/*
		おまじないを使ったらscanfとprintf関連注意！！！！！！！！！！！！
	*/
}