#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <chrono>
#define _USE_MATH_DEFINES
#include <cmath>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iostream>
#include <iterator>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
using namespace std;

#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

const int INF = 0x3f3f3f3f;
const long long LINF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-8;
const int MOD = 1000000007; // 998244353;
const int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
/*-------------------------------------------------*/
int main() {
  cin.tie(0); ios::sync_with_stdio(false);
  // freopen("input.txt", "r", stdin);

  int n, m, a; cin >> n >> m >> a;
  vector<map<int, int> > mp(n + 1);
  while (m--) {
    int l, r, p; cin >> l >> r >> p;
    mp[l][r] = p;
  }
  vector<vector<long long> > dp(n + 2, vector<long long>(2, -LINF));
  dp[1][1] = 0;
  FOR(i, 1, n + 1) {
    for (auto p : mp[i]) {
      dp[p.first + 1][1] = max({dp[p.first + 1][1], dp[i][1] + p.second - (p.first == n ? 0 : a)});
    }
    dp[i + 1][0] = max({dp[i + 1][0], dp[i][0], dp[i][1]});
    dp[i + 1][1] = max(dp[i + 1][1], max(dp[i][0], dp[i][1]) - a);
  }
  cout << max(dp[n + 1][0], dp[n + 1][1]) << '\n';
  return 0;
}