#include <bits/stdc++.h>
using namespace std;

int main() {
  ios::sync_with_stdio(false);

  int N, M, A; {
    cin >> N >> M >> A;
  }

  vector<vector<pair<int, int>>> pr(N + 1); {
    for (int i = 0; i < M; ++i) {
      int L, R, P;
      cin >> L >> R >> P;
      pr[L - 1].emplace_back(P, R);
    }
  }

  const int64_t INF = (int64_t) 1 << 60;
  vector<vector<int64_t>> d(N + 1, vector<int64_t>(2, -INF)); {
    d[0][1] = 0;
    for (int i = 0; i < N; ++i) {
      for (int j = 0; j < 2; ++j) {
        d[i + 1][0] = max(d[i + 1][0], d[i][j]);
        d[i + 1][1] = max(d[i + 1][1], d[i][j] - A);
        for (auto [p, r] : pr[i]) {
          if (j) d[r][1] = max(d[r][1], d[i][j] - A + p);
        }
      }
    }
  }

  int64_t res = max(d[N][0], d[N][1] + A);
  cout << res << endl;
}