#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)

const long long INF = 1LL<<60;
long long dp[100000+1][2];
vector<pair<int, int> > v[100000+1];

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n, m, a;
  cin >> n >> m >> a;

  for (int i = 0; i < m; i++) {
    int l, r, p;
    cin >> l >> r >> p;
    v[r].emplace_back(--l, p);
  }

  for (int i = 0; i <= n; i++)
    for (int j = 0; j < 2; j++)
      dp[i][j] = -INF;
  
  dp[0][0] = dp[0][1] = 0;

  for (int i = 1; i <= n; i++) {
    dp[i][0] = max(dp[i-1][0], dp[i-1][1]);
    for (auto &[l, p]: v[i]) {
      if (dp[l][1] != -INF)
        dp[i][1] = max(dp[i][1], dp[l][1] + p - (i == n ? 0 : a));
      dp[i][1] = max(dp[i][1], dp[l][0] + p - (i == n ? a : 2 * a));
    }
  }

  cout << max(dp[n][0], dp[n][1]) << endl;

  return 0;
}