#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;

int main(){
  int n, m, a;
  cin >> n >> m >> a;
  vector<vector<P>> v(n+1);
  for (int i = 0; i < m; i++) {
    int l, r, p;
    cin >> l >> r >> p;
    v[r].emplace_back(make_pair(l,p));
  }
  ll res = 0;
  vector<ll> dp(n+1,0);
  for (int i = 1; i <= n; i++) {
    dp[i] = res - a;
    for (auto x : v[i]) {
      dp[i] = max(dp[i], dp[x.first - 1] + x.second - (i == n ? 0 : a));
    }
    res = max(res, dp[i]);
  }
  cout << res << endl;
  return 0;
}