#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>>> segs(n + 1);
  for (int i = 0; i < m; i++) {
    int l, r, p;
    cin >> l >> r >> p;
    segs[r].emplace_back(l - 1, p);
  }
  auto dp = vector<vector<long long>>(n + 1, vector<long long>(2, -(1LL << 60)));
  dp[0][1] = 0;
  for (int r = 1; r <= n; r++) {
    dp[r][0] = max({dp[r][0], dp[r - 1][1], dp[r - 1][0]});
    for (auto i : segs[r]) {
      int l = i.first;
      long long p = i.second;
      dp[r][1] = max({dp[r][1], dp[l][0] + p - a - (r == n ? 0 : 1) * a, dp[l][1] + p - (r == n ? 0 : 1) * a});
    }
  }
  cout << max(dp[n][0], dp[n][1]) << endl;
  return 0;
}