import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] sa = br.readLine().split(" ");
		int n = Integer.parseInt(sa[0]);
		int m = Integer.parseInt(sa[1]);
		int a = Integer.parseInt(sa[2]);
		Map<Integer, List<Area>> map = new HashMap<>();
		for (int i = 0; i < m; i++) {
			sa = br.readLine().split(" ");
			Area area = new Area();
			area.l = Integer.parseInt(sa[0]);
			area.r = Integer.parseInt(sa[1]);
			area.p = Integer.parseInt(sa[2]);
			List<Area> list = map.get(area.r);
			if (list == null) {
				list = new ArrayList<>();
				map.put(area.r, list);
			}
			list.add(area);
		}
		br.close();

		long[] dp = new long[n + 1];
		long max = 0;
		for (int i = 1; i < n; i++) {
			List<Area> list = map.get(i);
			dp[i] = max - a;
			if (list != null) {
				long max1 = Long.MIN_VALUE;
				for (Area area : list) {
					long val = dp[area.l - 1] + area.p;
					max1 = Math.max(max1, val);
				}
				dp[i] = Math.max(dp[i], max1 - a);
			}
			max = Math.max(max, dp[i]);
		}

		List<Area> list = map.get(n);
		if (list != null) {
			long max1 = Long.MIN_VALUE;
			for (Area area : list) {
				long val = dp[area.l - 1] + area.p;
				max1 = Math.max(max1, val);
			}
			dp[n] = max1;
			max = Math.max(max, dp[n]);
		}
		System.out.println(max);
	}

	static class Area {
		int l, r, p;
	}
}