#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream>
#include <random>
#include<map>
#include <iomanip>
#include <time.h>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <cassert>
#include<fstream>
#include <unordered_map>
#include <cstdlib>
#include <complex>
using namespace std;
#define Ma_PI 3.141592653589793
#define eps 0.00000001
#define LONG_INF 1e18
#define GOLD 1.61803398874989484820458
#define MAX_MOD 1000000007
#define MOD 998244353
#define REP(i,n) for(long long i = 0;i < n;++i)    
#define seg_size 524288
long long gcd(long long a, long long b) {
	if (b == 0) return a;
	return gcd(b, a % b);
}
long long dp[2][200000];
vector<pair<long long,long long>> skipping[200000];
int main(){
#define int long long
	iostream::sync_with_stdio(false);
	int n, m, a;
	cin >> n >> m >> a;
	REP(i, m) {
		long long a, b, c;
		cin >> a >> b >> c;
		a--;
		skipping[a].push_back(make_pair(b, c));
	}
	REP(i, 2) {
		REP(q, 200000) {
			dp[i][q] = -LONG_INF;
		}
	}
	dp[1][0] = 0;
	for (int i = 0; i <= n; ++i) {
		dp[0][i + 1] = max({ dp[0][i + 1], dp[0][i],dp[1][i] });
		for (int q = 0; q < skipping[i].size(); ++q) {
			int next = skipping[i][q].first;
			long long value = skipping[i][q].second;
			int geko = 0;
			if (next != n) {
				geko = a;
			}
			dp[1][next] = max({ dp[1][next],dp[1][i] + value - geko,dp[0][i] + value - a - geko});
		}
	}
	cout << max(dp[0][n + 1], dp[1][n + 1]) << endl;
	return 0;
}