#include <bits/stdc++.h>
#define LLI long long int
#define FOR(v, a, b) for(LLI v = (a); v < (b); ++v)
#define FORE(v, a, b) for(LLI v = (a); v <= (b); ++v)
#define REP(v, n) FOR(v, 0, n)
#define REPE(v, n) FORE(v, 0, n)
#define REV(v, a, b) for(LLI v = (a); v >= (b); --v)
#define ALL(x) (x).begin(), (x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define ITR(it, c) for(auto it = (c).begin(); it != (c).end(); ++it)
#define RITR(it, c) for(auto it = (c).rbegin(); it != (c).rend(); ++it)
#define EXIST(c,x) ((c).find(x) != (c).end())
#define fst first
#define snd second
#define popcount __builtin_popcount
#define UNIQ(v) (v).erase(unique(ALL(v)), (v).end())
#define bit(i) (1LL<<(i))
#define sz(v) ((LLI)(v).size())

#ifdef DEBUG
#include <misc/C++/Debug.cpp>
#else
#define dump(...) ((void)0)
#endif

#define gcd __gcd

using namespace std;
template <class T> constexpr T lcm(T m, T n){return m/gcd(m,n)*n;}

template <typename I> void join(ostream &ost, I s, I t, string d=" "){for(auto i=s; i!=t; ++i){if(i!=s)ost<<d; ost<<*i;}ost<<endl;}
template <typename T> istream& operator>>(istream &is, vector<T> &v){for(auto &a : v) is >> a; return is;}
template <typename T, typename U> istream& operator>>(istream &is, pair<T,U> &p){is >> p.first >> p.second; return is;}

template <typename T, typename U> bool chmin(T &a, const U &b){return (a>b ? a=b, true : false);}
template <typename T, typename U> bool chmax(T &a, const U &b){return (a<b ? a=b, true : false);}
template <typename T, size_t N, typename U> void fill_array(T (&a)[N], const U &v){fill((U*)a, (U*)(a+N), v);}

LLI dp[100100][2];

const LLI inf = 1LL<<60;

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n,m,a;
  while(cin >> n >> m >> a){
    fill_array(dp, -inf);

    vector<vector<pair<int,int>>> segs(n+1);

    REP(i,m){
      int l,r,p; cin >> l >> r >> p;
      segs[r].push_back(make_pair(l,p));
    }

    dp[0][0] = 0;

    REP(i,n){
      chmax(dp[i+1][0], max(dp[i][0], dp[i][1]));

      for(auto &seg : segs[i+1]){
	int l = seg.fst;
	int p = seg.snd;

	
	chmax(dp[i+1][1], dp[l-1][0]+p-2*a + (l==1 ? a : 0) + (i+1==n ? a : 0));
	chmax(dp[i+1][1], dp[l-1][1]+p-a + (i+1==n ? a : 0));
      }
    }
    /*
    FORE(i,0,10){
      cerr << dp[i][0] << " " << dp[i][1] << endl;
    }
    */
    
    LLI ans = max(dp[n][0], dp[n][1]);
    cout << ans << endl;
    
  }
  
  return 0;
}