#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
long long op(long long a, long long b) { return max(a, b); }
long long e() { return -LINF; }
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n, m, a; cin >> n >> m >> a;
	segtree<long long, op, e>seg(n + 1);//最後に引いた所
	seg.set(0, 0);
	rep2(i, 1, n)seg.set(i, -a);
	vector<vector<P>>v(n);
	rep(i, m) {
		int l, r, p; cin >> l >> r >> p;
		l--, r--;
		v[l].push_back({ r,p });
	}
	rep(i, n) {
		{
			long long val = seg.prod(0, i);
			rep(j, v[i].size()) {
				long long nval = val - a * 2 + v[i][j].second;
				if (v[i][j].first == n - 1)nval += a;
				long long get = seg.get(v[i][j].first + 1);
				if (nval > get)seg.set(v[i][j].first + 1, nval);
			}
		}
		{
			long long val = seg.get(i);
			rep(j, v[i].size()) {
				long long nval = val - a + v[i][j].second;
				if (v[i][j].first == n - 1)nval += a;
				long long get = seg.get(v[i][j].first + 1);
				if (nval > get)seg.set(v[i][j].first + 1, nval);
			}
		}
	}
	long long ans = seg.all_prod();
	cout << ans << endl;
	return 0;
}