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

#define rep(i,j,n) for(int i=j;i<n;++i)
#define all(i) i.begin(),i.end()
#define rall(i) i.rbegin(), i.rend()
#define INF 1e9
#define LINF 1e18
const int mod = 1e9 + 7;

typedef long long i64;
typedef pair<int, int> pi;

template <class T> using vt = vector<T>;
template <class T> using vvt = vector<vector<T>>;

i64 gcd(i64 n, i64 m) {return (m == 0? n : gcd(m, n % m));}
i64 lcd(i64 n, i64 m) {return (n / gcd(n, m) * m);}
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n, m, a;
  cin >> n >> m >> a;
  vvt<pi> next(n + 1);
  rep(i, 0, m) {
    int l, r, p;
    cin >> l >> r >> p;
    next[r].push_back({l, p});
  }

  vt<i64> dp(n + 1, 0);
  i64 Max = 0;
  rep(i, 1, n + 1) {
    dp[i] = Max - a;
    for(auto &nxt : next[i]) {
      int s = nxt.second - a;
      if(i == n) s += a;
      dp[i] = max(dp[i], dp[nxt.first - 1] + s);
    }
    Max = max(Max, dp[i]);
  }
  cout << Max << endl;
}