#include <bits/stdc++.h>
using i64 = long long;

int main() {
  unsigned n, m;
  i64 a;
  std::cin >> n >> m >> a;
  std::vector<std::pair<std::pair<unsigned, unsigned>, i64>> v;
  for (unsigned i = 0; i < m; i++) {
    int l, r;
    i64 p;
    std::cin >> l >> r >> p;
    v.emplace_back(std::piecewise_construct, std::make_tuple(r, l), std::make_tuple(p));
  }
  std::sort(v.begin(), v.end());

  std::vector<std::vector<i64>> dp(n + 1, std::vector<i64>(2));
  for (unsigned i = 1, j = 0; i <= n; i++) {
    dp[i][0] = std::max(dp[i - 1][0], dp[i - 1][1]);
    dp[i][1] = dp[1][0] - a;
    while (j < m && v[j].first.first == i) {
      dp[i][1] = std::max({
            dp[i][1],
            dp[v[j].first.second - 1][0] + v[j].second - a * 2,
            dp[v[j].first.second - 1][1] + v[j].second - a
          });
      j++;
    }
  }

  std::cout << std::max(dp[n][0], dp[n][1] + a) << std::endl;

  return 0;
}