using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using SB = System.Text.StringBuilder;
//using System.Threading.Tasks;
//using System.Text.RegularExpressions;
//using System.Globalization;
//using System.Diagnostics;
using static System.Console;
using System.Numerics;
using static System.Math;
using pair = Pair<int, int>;

class Program
{
    static void Main()
    {
        //SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false });
        new Program().solve();
        Out.Flush();
    }
    readonly Scanner cin = new Scanner();
    readonly int[] dd = { 0, 1, 0, -1, 0 }; //→↓←↑
    readonly int mod = 1000000007;
    readonly int dom = 998244353;
    bool chmax<T>(ref T a, T b) where T : IComparable<T> { if (a.CompareTo(b) < 0) { a = b; return true; } return false; }
    bool chmin<T>(ref T a, T b) where T : IComparable<T> { if (b.CompareTo(a) < 0) { a = b; return true; } return false; }


    class Edge : IComparable<Edge>
    {
        public int from, to, id; public long cost;
        public Edge(int from, int to, long cost, int id = -1)
        {
            this.from = from;
            this.to = to;
            this.cost = cost;
            this.id = id;
        }
        public int CompareTo(Edge e) => cost.CompareTo(e.cost);
    }


    void solve()
    {
        int N = cin.nextint;
        int M = cin.nextint;
        var A = cin.nextlong;
        var E = new Edge[M];
        for (int i = 0; i < M; i++)
        {
            E[i] = new Edge(cin.nextint - 1, cin.nextint, cin.nextlong);
        }

        E = E.OrderBy(i => i.to).ThenBy(i => i.from).ToArray();

        var dp = new long[N + 1];
        var S = new SegTree<long>(N + 1, Max, 0);
        foreach (var e in E)
        {
            int L = e.from;
            int R = e.to;
            long P = e.cost;


            if (R == N)
            {
                chmax(ref dp[R], S[0, L] - A + P);
                if(dp[L] > 0) chmax(ref dp[R], dp[L] + P);
            }
            else if (L == 0)
            {
                chmax(ref dp[R], P - A);
            }
            else
            {
                chmax(ref dp[R], S[0, L] - 2 * A + P);
                if (dp[L] > 0) chmax(ref dp[R], dp[L] - A + P);
            }

            S.Update(R, dp[R]);

            //WriteLine();
            //dp.join();
            //S.Items.join();
            //WriteLine();
        }

        WriteLine(S[0, N]);
    }

}

/// <OriginalAuthor>riantkb</OriginalAuthor>
class SegTree<T>
{
    readonly int n;
    int s, t;
    T[] tr;
    readonly Func<T, T, T> f;
    readonly T exnum;

    /// <summary>
    ///  セグメントツリーの構築1
    /// </summary>
    /// <param name="m">要素数</param>
    /// <param name="f">マージ関数</param>
    /// <param name="ex">単位元</param>
    public SegTree(int m, Func<T, T, T> f, T ex)
    {
        this.f = f; exnum = ex; n = 1;
        while (n < m) n <<= 1;
        tr = new T[(n << 1) - 1];
        for (int i = 0; i < tr.Length; i++) tr[i] = ex;
    }
    public SegTree(int m, Func<T, T, T> f, T ex, T ini) : this(m, f, ex)
    {
        for (int i = 0; i < m; i++) Assign(i, ini);
        All_Update();
    }
    public SegTree(int m, Func<T, T, T> f, T ex, IList<T> ini) : this(m, f, ex)
    {
        for (int i = 0; i < m; i++) Assign(i, ini[i]);
        All_Update();
    }
    public T Look(int j) => tr[j + n - 1];
    public T Peek() => tr[0];


    /// <summary>
    /// 最下層に値の代入
    /// </summary>
    /// <param name="j">代入するインデックス</param>
    /// <param name="x">代入する値</param>
    public void Assign(int j, T x) => tr[j + n - 1] = x;
    public void Update(int j, T x)
    {
        Assign(j, x);
        Update(j);
    }
    public void Update(int j)
    {
        int i = j + n - 1;
        while (i > 0) { i = i - 1 >> 1; tr[i] = f(tr[i << 1 | 1], tr[i + 1 << 1]); }
    }
    public void All_Update() { for (int i = n - 2; i >= 0; i--) tr[i] = f(tr[i << 1 | 1], tr[i + 1 << 1]); }
    /// <summary>
    /// return node[s, t] 区間クエリ
    /// </summary>
    /// <param name="s">左端 0-indexed</param>
    /// <param name="t">右端 0-indexed</param>
    /// <returns>node[s, t]</returns>
    public T this[int s, int t] => Run(s, t);
    T Run(int s, int t) { t++; this.s = s; this.t = t; return Query(0, 0, n); }
    T Query(int k, int l, int r) => r <= s || t <= l ? exnum : s <= l && r <= t ? tr[k]
                              : f(Query(k << 1 | 1, l, l + r >> 1), Query(k + 1 << 1, l + r >> 1, r));
    public T[] Items
    {
        get
        {
            var ret = new T[n];
            for (int i = 0; i < ret.Length; i++)
            {
                ret[i] = Run(i, i);
            }
            return ret;
        }
    }

}

static class Ex
{
    public static void join<T>(this IEnumerable<T> values, string sep = " ") => WriteLine(string.Join(sep, values));
    public static string concat<T>(this IEnumerable<T> values) => string.Concat(values);
    public static string reverse(this string s) { var t = s.ToCharArray(); Array.Reverse(t); return t.concat(); }

    public static int lower_bound<T>(this IList<T> arr, T val) where T : IComparable<T>
    {
        int low = 0, high = arr.Count;
        int mid;
        while (low < high)
        {
            mid = ((high - low) >> 1) + low;
            if (arr[mid].CompareTo(val) < 0) low = mid + 1;
            else high = mid;
        }
        return low;
    }
    public static int upper_bound<T>(this IList<T> arr, T val) where T : IComparable<T>
    {
        int low = 0, high = arr.Count;
        int mid;
        while (low < high)
        {
            mid = ((high - low) >> 1) + low;
            if (arr[mid].CompareTo(val) <= 0) low = mid + 1;
            else high = mid;
        }
        return low;
    }
}

class Pair<T, U> : IComparable<Pair<T, U>> where T : IComparable<T> where U : IComparable<U>
{
    public T f; public U s;
    public Pair(T f, U s) { this.f = f; this.s = s; }
    public int CompareTo(Pair<T, U> a) => f.CompareTo(a.f) != 0 ? f.CompareTo(a.f) : s.CompareTo(a.s);
    public override string ToString() => $"{f} {s}";
}

class Scanner
{
    string[] s; int i;
    readonly char[] cs = new char[] { ' ' };
    public Scanner() { s = new string[0]; i = 0; }
    public string[] scan => ReadLine().Split();
    public int[] scanint => Array.ConvertAll(scan, int.Parse);
    public long[] scanlong => Array.ConvertAll(scan, long.Parse);
    public double[] scandouble => Array.ConvertAll(scan, double.Parse);
    public string next
    {
        get
        {
            if (i < s.Length) return s[i++];
            string st = ReadLine();
            while (st == "") st = ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            i = 0;
            return next;
        }
    }
    public int nextint => int.Parse(next);
    public long nextlong => long.Parse(next);
    public double nextdouble => double.Parse(next);
}