#include <algorithm>
#include <cmath>
#include <complex>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <vector>
#include <functional>
#include <cstring>
#include <regex>
#include <random>
#include <cassert>
#include <stack>
using namespace std;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, s, n) for (int i = (s); i < (int)(n); i++)
#define revrep(i, n) for (int i = (n) - 1; i >= 0; i--)
#define revrepr(i, s, n) for (int i = (n) - 1; i >= s; i--)
#define debug(x) cerr << #x << ": " << x << "\n"
#define popcnt(x) __builtin_popcount(x)

using ll = long long;
using P = pair<int, int>;

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; }

template<class T>
istream& operator >>(istream &is, vector<T> &v) {
    for (int i = 0; i < (int)v.size(); i++) cin >> v.at(i);
    return is;
}

template<class T, class U>
ostream& operator <<(ostream &os, pair<T, U> p) {
    cout << '(' << p.first << ", " << p.second << ')';
    return os;
}

template<class T>
void print(const vector<T> &v, const string &delimiter) { rep(i, v.size()) cout << (0 < i ? delimiter : "") << v.at(i); cout << endl; }

template<class T>
void print(const vector<vector<T>> &vv, const string &delimiter) { for (const auto &v: vv) print(v, delimiter); }

struct Query {
    P seg;
    ll p;
};
bool operator <(const Query &a, const Query &b) { return a.seg < b.seg; }

int n, m, a;
vector<Query> qs;

const ll INF = 1e18;
vector<vector<ll>> memo(100001, vector<ll>(2, -INF));

ll solve(int idx, int done_left) {
    if (memo[idx][done_left] != -INF) return memo[idx][done_left];
    
    Query q = qs[idx];
    
    ll res1 = q.p - (2 - done_left) * a;
    if (q.seg.second == n) res1 += a;
    int nxt_idx = lower_bound(qs.begin() + idx + 1, qs.end(), Query{P(q.seg.second + 1, -1), -1}) - qs.begin();
    if (nxt_idx < m) {
        if (q.seg.second + 1 == qs[nxt_idx].seg.first) res1 += solve(nxt_idx, 1);
        else res1 += solve(nxt_idx, 0);
    }
    
    ll res2 = 0;
    if (idx + 1 < m) {
        if (done_left && q.seg.first == qs[idx + 1].seg.first) res2 += solve(idx + 1, 1);
        else res2 += solve(idx + 1, 0);
    }
    
    return memo[idx][done_left] = max(res1, res2);
}

int main() {
    cin >> n >> m >> a;
    n--;
    qs.resize(m);
    rep(i, m) {
        int l, r, p;
        cin >> l >> r >> p;
        l--; r--;
        qs[i] = Query{P(l, r), p};
    }
    sort(qs.begin(), qs.end());
    
    cout << solve(0, 1) << endl;
}