#include <bits/stdc++.h>
template<typename T1, typename T2>
inline bool cmx (T1& a, T2 b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
int main() {
  std::cin.tie(0); std::cin.sync_with_stdio(false);
  int n, m, a; std::cin >> n >> m >> a;
  std::vector<std::tuple<int, int, int>> itv;
  while (m--) {
    int l, r, p; std::cin >> l >> r >> p;
    l--;
    itv.emplace_back(l, r, p);
  }
  std::sort(itv.begin(), itv.end());
  std::vector<long long> dp (n + 1, -a);
  std::vector<long long> cum(n + 1, -a);
  dp[0] = 0;
  int now = 1;
  for (auto [l, r, p] : itv) {
    for (; now <= l; now++) {
      cum[now] = std::max(cum[now - 1], dp[now - 1]);
    }
    cmx(dp[r],  dp[l] + p - a);
    cmx(dp[r], cum[l] + p - a * 2);
  }
  for (; now <= n; now++) {
    cum[now] = std::max(cum[now - 1], dp[now - 1]);
  }
  long long ret = std::max(cum[n], dp[n] + a);
  std::cout << ret << std::endl;
  return 0;
}