#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <vector>

using namespace std;
typedef long long ll;

struct Range {
  int l;
  int r;
  ll p;

  Range(int l = -1, int r = -1, ll p = 0) {
    this->l = l;
    this->r = r;
    this->p = p;
  }
};

int main() {
  int N, M;
  ll A;
  cin >> N >> M >> A;

  vector<Range> range_list[N + 1];
  for (int i = 0; i < M; ++i) {
    Range range;
    cin >> range.l >> range.r >> range.p;

    range_list[range.l].push_back(range);
  }

  vector<vector<ll>> dp(N + 2, vector<ll>(2, LLONG_MIN));
  dp[1][1] = 0;

  for (int i = 1; i <= N; ++i) {
    dp[i][0] = max(dp[i][0], dp[i - 1][0]);
    dp[i][0] = max(dp[i][0], dp[i - 1][1]);

    for (int j = 0; j < 2; ++j) {
      if (dp[i][j] == LLONG_MIN) continue;

      for (Range &range : range_list[i]) {
        if (j == 0) {
          if (range.r == N) {
            dp[range.r + 1][1] = max(dp[range.r + 1][1], dp[i][j] + range.p - A);
          } else {
            dp[range.r + 1][1] = max(dp[range.r + 1][1], dp[i][j] + range.p - 2 * A);
          }
        } else {
          if (range.r == N) {
            dp[range.r + 1][1] = max(dp[range.r + 1][1], dp[i][j] + range.p);
          } else {
            dp[range.r + 1][1] = max(dp[range.r + 1][1], dp[i][j] + range.p - A);
          }
        }
      }
    }
  }

  ll ans = 0;

  for (int i = 1; i <= N + 1; ++i) {
    for (int j = 0; j < 2; ++j) {
      ans = max(ans, dp[i][j]);
    }
  }

  cout << ans << endl;

  return 0;
}