#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
signed main() { 
  ios::sync_with_stdio(false); cin.tie(0); 
  int n, m, a;
  cin >> n >> m >> a;
  vector<vector<pair<int, int>>> rr(n + 1);
  for (int i = 0; i < m; i++) {
    int l, r, p;
    cin >> l >> r >> p;
    rr[r].emplace_back(l - 1, p);
  }
  vector<long long> dp(n + 1), s(n + 1);
  s[0] = 1;
  s[n] = 1;
  for (int r = 1; r <= n; r++) {
    dp[r] = max(dp[r - 1], dp[r]);
    long long tmp = dp[r];
    for (auto i : rr[r]) {
      int l = i.first;
      long long p = i.second;
      long long t = dp[l] + p - (r == n ? 0 : 1) * a;
      dp[r] = max(dp[r], t - (s[l] ? 0 : 1) * a);
    }
    if (dp[r] > tmp) s[r] = 1;
  }
  cout << dp[n] << endl;
  return 0;
}