#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<ll, ll> p_ll;

template<class T>
void debug(T itr1, T itr2) { auto now = itr1; while(now<itr2) { cout << *now << " "; now++; } cout << endl; }
#define repr(i,from,to) for (ll i=(ll)from; i<(ll)to; i++)
#define all(vec) vec.begin(), vec.end()
#define rep(i,N) repr(i,0,N)
#define per(i,N) for (int i=(int)N-1; i>=0; i--)

const ll MOD = pow(10,9)+7;
const ll LLINF = pow(2,61)-1;
const int INF = pow(2,30)-1;

vector<ll> fac;
void c_fac(int x=pow(10,6)+10) { fac.resize(x,true); rep(i,x) fac[i] = i ? (fac[i-1]*i)%MOD : 1; }
ll inv(ll a, ll m=MOD) { ll b = m, x = 1, y = 0; while (b!=0) { int d = a/b; a -= b*d; swap(a,b); x -= y*d; swap(x,y); } return (x+m)%m; }
ll nck(ll n, ll k) { return fac[n]*inv(fac[k]*fac[n-k]%MOD)%MOD; }
ll gcd(ll a, ll b) { if (a<b) swap(a,b); return b==0 ? a : gcd(b, a%b); }
ll lcm(ll a, ll b) { return a/gcd(a,b)*b; }

struct range { 
  ll l, r, p; 
  bool operator< (const range &x) const {return l<x.l||(l==x.l&&r<x.r);};
};

int main() {
  ll N, M, A; cin >> N >> M >> A;
  range r[M]; rep(i,M) { cin >> r[i].l >> r[i].r >> r[i].p; r[i].l--; }
  sort(r,r+M);
  // rep(i,M) cout << r[i].l << "-" << r[i].r << " " << r[i].p << endl;

  ll dp[N+1][2] = {}; repr(i,1,N+1) dp[i][1] = -1*A; 
  ll np = 0;
  rep(i,N+1) {
    while(np!=M&&r[np].l==i) {
      ll to = r[np].r==N ? dp[i][1]+r[np].p : dp[i][1]+r[np].p-A;
      dp[r[np].r][1] = max(dp[r[np].r][1], to);
      np++;
    }
    dp[i+1][0] = max(dp[i+1][0], max(dp[i][0], dp[i][1]));
    dp[i+1][1] = max(dp[i+1][1], max(dp[i][0], dp[i][1])-A);
  }

  // rep(i,N+1) cout << dp[i][0] << " " << dp[i][1] << endl;
  ll result = max(dp[N][0], dp[N][1]);
  cout << result << endl;
  return 0;
}