#include<iostream>
#include<vector>
#include<string>
#include<cmath>
#include<algorithm>
#include<functional>
#include<numeric>
#include<queue>
#include<stack>
#include<map>
#include<unordered_map>
#include<set>
#include<bitset>
#include<random>

#pragma region
using namespace std;
#define FOR(i,r,n) for(ll i = (ll)(r); i < (ll)(n); i++)
#define rep(i,n) FOR(i,0LL,n)
#define RFOR(i,r,n) for(ll i=(ll)(n-1);i>=r;i--)
#define rrep(i,n) RFOR(i,0LL,n)
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define COUNT(a,y,x) upper_bound(all(a), y) - lower_bound(all(a), x)
#define UNIQUE(a) sort(all(a)); a.erase(unique(all(a)), a.end())
#define pb push_back
typedef long long int ll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef pair<ll, ll> pll;
typedef vector<pll> vpll;
typedef vector<string> vs;
typedef map<ll, ll> MAP;
const ll inf = 1LL << 61;
const ll mod = 1000000007LL;
//const ll mod = 998244353LL;

ll n = 0, m = 0, ans = 0, tmp = 0, ma = -inf, mi = inf;
string s;
bool ok;
ll dx[9] = { 0,1,0,-1,0,1,1,-1,-1 }, dy[9] = { 0,0,1,0,-1,1,-1,1,-1 };
#define endl '\n'
#pragma endregion
#define MAX 222222


ll smax[MAX][2];


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


  ll a;
  cin >> n >> m >> a;
  vector<pair<pll, ll>> v;
  rep(i, m) {
    ll l, r, p;
    cin >> l >> r >> p;
    v.pb(make_pair(pll(r, l), p));
  }
  sort(all(v));
  ll idx = 0;
  rep(i, n + 1) smax[i][1] = -inf;
  rep(i, n + 1) {
    while (idx < m&&v[idx].first.first == i) {
      ll le = v[idx].first.second, ri = v[idx].first.first, p = v[idx].second;
      if (ri == n && le == 1) smax[ri][1] = max(smax[ri][1], smax[le - 1][0] + p);
      else if (ri == n) smax[ri][1] = max(smax[ri][1], max(smax[le - 1][1] + p, smax[le - 1][0] + p - a));
      else if (le == 1) smax[ri][1] = max(smax[ri][1], smax[le - 1][0] + p - a);
      else smax[ri][1] = max(smax[ri][1], max(smax[le - 1][1] + p - a, smax[le - 1][0] + p - 2 * a));
      idx++;
    }
    smax[i][0] = max(smax[max(0LL, i - 1)][1], smax[max(0LL, i - 1)][0]);
  }

  cout << max(smax[n][0], smax[n][1]) << endl;


  return 0;
}