#include <bits/stdc++.h>
using namespace std;
using lint = long long;
template<class T = int> using V = vector<T>;
template<class T = int> using VV = V< V<T> >;

int main() {
  cin.tie(nullptr); ios::sync_with_stdio(false);
  int n, m, a; cin >> n >> m >> a;
  struct S { int l, p; };
  VV<S> d(n + 1);
  while (m--) {
    int l, r, p; cin >> l >> r >> p, --l;
    d[r].emplace_back(S{l, p});
  }
  V<lint> dp(n + 1, -1e18);
  dp[0] = 0;
  lint mx = 0;
  for (int i = 1; i <= n; ++i) {
    dp[i] = mx - a;
    for (S e : d[i]) {
      dp[i] = max(dp[i], dp[e.l] + e.p - a);
    }
    mx = max(mx, dp[i]);
  }
  dp[n] += a;
  cout << *max_element(begin(dp), end(dp)) << '\n';
}