#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>

using namespace std;

#define int long long
#define rep(i,n) for(int i = 0; i < (n); i++)
#define endl "\n"

const long long INF = (long long)1e18;
const long long MOD = (long long)1e9 + 7; 

string yn(bool f){return f?"Yes":"No";}
string YN(bool f){return f?"YES":"NO";}

#define MAX 110000

vector<pair<int,int>> num[MAX];

signed main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(10);
	
	int N, M, A;
	int l, r, p;
	static int dp[MAX][3];
	cin>>N>>M>>A;
	

	
	for(int i = 0; i < M; i++){
		cin>>l>>r>>p;
		num[r].push_back(make_pair(l-1, p));
	}
	
	for(int i = 1; i <= N; i++){
		if(N == i){
			int max_ = -INF;
			max_ = max(max_, dp[i-1][1]);
			max_ = max(max_, dp[i-1][0]);
			dp[i][0] = max(0ll,max(dp[i-1][1], dp[i-1][0]));
			for(int j = 0; j < num[i].size(); j++){
				max_ = max(dp[num[i][j].first][0] - A + num[i][j].second, max_);
				max_ = max(dp[num[i][j].first][1] + num[i][j].second, max_);
				// cout<<num[i][j].first<<" "<<num[i][j].second<<endl;
			}
			dp[i][1] = max_;
		} else {
			int max_ = -INF, max2 = 0;
			max_ = max(max_, dp[i-1][1] - A);
			max_ = max(max_, dp[i-1][0] - A);
			dp[i][0] = max(0ll,max(dp[i-1][1], dp[i-1][0]));
			for(int j = 0; j < num[i].size(); j++){
				max_ = max(dp[num[i][j].first][0] - A*2 + num[i][j].second, max_);
				max_ = max(dp[num[i][j].first][1] - A + num[i][j].second, max_);
			}
			dp[i][1] = max_;
		}
		// cout<<"i = "<<i<<" "<<dp[i][0]<<" "<<dp[i][1]<<endl;
	}
	
	cout<<max(dp[N][0], dp[N][1])<<endl;
	
	return 0;
}