#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
using namespace std;

using ll = long long;
using P = pair<int, int>;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

template<typename Monoid>
struct SegmentTree{
    using F = function<Monoid(Monoid, Monoid)>;

    int sz;
    vector<Monoid> seg;

    const F f;
    const Monoid M1;

    SegmentTree(const F f, const Monoid& M1) : f(f), M1(M1) {}

    SegmentTree(int n, const F f, const Monoid &M1) : f(f), M1(M1) {
        sz = 1;
        while(sz < n)   sz <<= 1;
        seg.assign(2 * sz, M1);
    }

    void resize(int n){
        sz = 1;
        while(sz < n)   sz <<= 1;
        seg.assign(2 * sz, M1);
    }

    void set(int k, const Monoid &x){
        seg[k + sz] = x;
    }

    void build(){
        for(int k = sz - 1; k > 0; --k){
            seg[k] = f(seg[k << 1], seg[k << 1 | 1]);
        }
    }

    void update(int k, const Monoid &x){
        k += sz;
        seg[k] = x;
        while(k >>= 1){
            seg[k] = f(seg[k << 1], seg[k << 1 | 1]);
        }
    }

    Monoid query(int a, int b){
        Monoid L = M1, R = M1;
        for(a += sz, b += sz; a < b; a >>= 1, b >>= 1){
            if(a & 1)   L = f(L, seg[a++]);
            if(b & 1)   R = f(seg[--b], R);
        }
        return f(L, R);
    }

    Monoid operator[](const int &k) const{
        return seg[k + sz];
    }

    // (type = true) : find_last
    // (type = false) : find_first
    template<typename C>
    int find_subtree(int a, const C &check, Monoid &M, bool type){
        while(a < sz){
            Monoid nxt = type ? f(seg[a << 1 | type], M) : f(M, seg[a << 1 | type]);
            if(check(nxt))  a = a << 1 | type;
            else M = nxt, a = 2 * a + 1 - type;
        }
        return a - sz;
    }

    template<typename C>
    int find_first(int a, const C &check){
        Monoid L = M1;
        if(a <= 0){
            if(check(f(L, seg[1]))) return find_subtree(1, check, L, false);
            return -1;
        }
        int b = sz;
        for(a += sz, b += sz; a < b; a >>= 1, b >>= 1){
            if(a & 1){
                Monoid nxt = f(L, seg[a]);
                if(check(nxt))  return find_subtree(a, check, L, false);
                L = nxt;
                ++a;
            }
        }
        return -1;
    }

    template<typename C>
    int find_last(int b, const C &check){
        Monoid R = M1;
        if(b >= sz){
            if(check(f(seg[1], R))) return find_subtree(1, check, R, true);
            return -1;
        }
        int a = sz;
        for(b += sz; a < b; a >>= 1, b >>= 1){
            if(b & 1){
                Monoid nxt = f(seg[--b], R);
                if(check(nxt))  return find_subtree(b, check, R, true);
                R = nxt;
            }
        }
        return -1;
    }
};

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int N, M, A;
    cin >> N >> M >> A;
    vector<vector<P>> rights(N);
    for(int i = 0; i < M; ++i){
        int l, r, p;
        cin >> l >> r >> p;
        rights[l - 1].emplace_back(r, p);
    }

    constexpr ll inf = 1e+17;
    SegmentTree<ll> seg(N + 1, [](ll a, ll b){return max(a, b);}, -inf);
    seg.update(0, 0LL);
    for(int l = 0; l < N; ++l){
        ll score = seg.query(0, l) - A;
        if(seg[l] > score)  score = seg[l];
        for(auto [r, p] : rights[l]){
            ll next_score = score + p + (r == N ? 0 : -A);
            if(next_score > seg[r]){
                seg.update(r, next_score);
            }
        }
    }

    cout << seg.query(0, N + 1) << endl;

    return 0;
}