// #define DEBUGGING
#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define ALL(V) (V).begin(), (V).end()
#define ALLR(V) (V).rbegin(), (V).rend()

template <typename T> using V = vector<T>;
template <typename T> using VV = V<V<T>>;
template <typename T, typename U> using P = pair<T, U>;
using ll = int64_t;
using PLL = P<ll, ll>;

template <typename T> const T& var_min(const T &t) { return t; }
template <typename T> const T& var_max(const T &t) { return t; }
template <typename T, typename... Tail> const T& var_min(const T &t, const Tail&... tail) { return min(t, var_min(tail...)); }
template <typename T, typename... Tail> const T& var_max(const T &t, const Tail&... tail) { return max(t, var_max(tail...)); }
template <typename T, typename... Tail> void chmin(T &t, const Tail&... tail) { t = var_min(t, tail...); }
template <typename T, typename... Tail> void chmax(T &t, const Tail&... tail) { t = var_max(t, tail...); }
template <typename T> const T& clamp(const T &t, const T &low, const T &high) { return max(low, min(high, t)); }
template <typename T> void chclamp(T &t, const T &low, const T &high) { t = clamp(t, low, high); }

namespace init__ {

struct InitIO {
    InitIO() {
        cin.tie(nullptr);
        ios_base::sync_with_stdio(false);
        cout << fixed << setprecision(30);
    }
} init_io;

}

#ifdef DEBUGGING
#include "../debug.cpp"
#else
#define DEBUG(...) 0
#define DEBUG_SEPARATOR_LINE 0
#endif

template <typename T>
T make_v(T init) { return init; }

template <typename T, typename... Tail>
auto make_v(T init, size_t s, Tail... tail) {
#define rec make_v(init, tail...)
    return V<decltype(rec)>(s, rec);
#undef rec
}

int main() {
    ll N, M, A;
    cin >> N >> M >> A;
    VV<PLL> rp(1e5 + 10);
    for(ll i = 0; i < M; i++) {
        ll l, r, p;
        cin >> l >> r >> p;
        l--;
        rp[l].emplace_back(r, p);
    }
    V<PLL> dp(N + 2, PLL(0, -A));
    dp[0].second = 0;
    for(ll i = 0; i < N; i++) {
        chmax(dp[i + 1].first, dp[i].first, dp[i].second);
        chmax(dp[i + 1].second, dp[i].first - (i + 1 == N ? 0 : A), dp[i].second - (i + 1 == N ? 0 : A));
        for(auto P : rp[i]) {
            ll r, p;
            tie(r, p) = P;
            ll nxt_p0 = dp[i].first + p - (r == N ? 0 : A) - (i == 0 ? 0 : A);
            ll nxt_p1 = dp[i].second + p - (r == N ? 0 : A);
            chmax(dp[r].second, nxt_p0, nxt_p1);
        }
    }
    DEBUG(dp);
    cout << max(dp[N].first, dp[N].second) << endl;
    return 0;
}