// IO
#include <cstdio>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm
#include <algorithm>
#include <cmath>
#include <numeric>

// container
#include <vector>
#include <string>
#include <tuple>
#include <set>
#include <map>
#include <unordered_map>
#include <stack>
#include <queue>
#include <deque>

// others
#include <random>
#include <limits>
#include <functional>
#include <ctime>
#include <cassert>

// type alias
using lint = long long;
using ldouble = long double;
template <class T>
using greater_priority_queue = std::priority_queue<T, std::vector<T>, std::greater<T>>;


/* ----- class ----- */

template <class Cost = int>
struct Edge {
    int src, dst;
    Cost cost;
    Edge(int src = -1, int dst = -1, Cost cost = 1)
        : src(src), dst(dst), cost(cost){};

    bool operator<(const Edge<Cost>& e) const { return this->cost < e.cost; }
    bool operator>(const Edge<Cost>& e) const { return this->cost > e.cost; }
};

template <class Cost = int>
using Edges = std::vector<Edge<Cost>>;

template <class Cost = int>
using Graph = std::vector<std::vector<Edge<Cost>>>;


/* ----- debug ----- */

#if __has_include("../setting/source/debug.hpp")
#include "../setting/source/debug.hpp"
#endif


/* ----- short functions ----- */

template <class T>
inline T sq(T a) { return a * a; }

template <class T>
inline T iceil(T n, T d) { return (n + d - 1) / d; }

template <class T>
T gcd(T a, T b) {
    while (b > 0) {
        a %= b;
        std::swap(a, b);
    }
    return a;
}

template <class T, class U>
T ipow(T b, U n) {
    T ret = 1;
    while (n > 0) {
        if (n & 1) ret *= b;
        n >>= 1;
        b *= b;
    }
    return ret;
}

// 0-indexed
template <class T, class U>
inline T kthbit(T a, U k) { return (a >> k) & 1; }

template <class T, class U>
inline T mask(T a, U k) { return a & ((1 << k) - 1); }

template <class T>
std::map<T, int> compress(std::vector<T>& v) {
    std::sort(v.begin(), v.end());
    v.erase(std::unique(v.begin(), v.end()), v.end());

    std::map<T, int> rev;
    for (int i = 0; i < v.size(); ++i) rev[v[i]] = i;
    return rev;
}

template <class T>
T Vec(T v) { return v; }

template <class T, class... Ts>
auto Vec(size_t l, Ts... ts) {
    return std::vector<decltype(Vec<T>(ts...))>(l, Vec<T>(ts...));
}


/* ----- constants ----- */

// const int INF = std::numeric_limits<int>::max() / 3;
const lint INF = std::numeric_limits<lint>::max() / 3;
// const ldouble PI = acos(-1);
// const ldouble EPS = 1e-10;
// std::mt19937 mt(int(std::time(nullptr)));


using namespace std;

struct Seg {
    int l, r;
    lint p;
    Seg(int l = 0, int r = 0, lint p = 0) : l(l), r(r), p(p) {}
    bool operator<(const Seg& a) const {
        return l == a.l ? r < a.r : l < a.l;
    }
};

int main() {
    int N, M, A;
    cin >> N >> M >> A;

    vector<Seg> segs(M);
    for (auto& s : segs) {
        cin >> s.l >> s.r >> s.p;
    }
    sort(segs.begin(), segs.end());

    auto dp = Vec<lint>(M + 1, 2, 0LL);
    dp[0][0] = -INF;
    // dp[i][b] = [0, i)まで見て、
    //            segs[i].lの左に線が引かれて[いる/いない]ときの最適解

    for (int i = 0; i < M; ++i) {
        // iを使わない場合
        dp[i + 1][0] = max({dp[i + 1][0], dp[i][0], dp[i][1]});

        // iを使う場合
        // segs[i]とsegs[j]が交わらない最小のjを求める
        int j = lower_bound(segs.begin(), segs.end(), Seg(segs[i].r + 1, -1)) -
                segs.begin();

        int cost = A * 2;
        if (segs[i].r == N) cost -= A;

        bool b = (segs[j].l == segs[i].r + 1);
        dp[j][b] = max({dp[j][b],
                        dp[i][0] + segs[i].p - cost,
                        dp[i][1] + segs[i].p - (cost - A)});
    }

    cout << max(dp[M][0], dp[M][1]) << endl;
    return 0;
}