#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}

int main() {
	int n = ri();
	int m = ri();
	int a = ri();
	int l[m], r[m], p[m];
	for (int i = 0; i < m; i++) l[i] = ri() - 1, r[i] = ri() - 1, p[i] = ri();
	std::map<int, int> ranges[n];
	for (int i = 0; i < m; i++) ranges[l[i]].insert({r[i], p[i]});
	int64_t dp[n + 1];
	for (int i = 0; i <= n; i++) dp[i] = -1000000007;
	dp[0] = 0;
	for (int i = 0; i < n; i++) {
		for (int j = i + 1; j <= n; j++) {
			dp[j] = std::max(dp[j], dp[i] - a);
		}
		for (auto j : ranges[i]) dp[j.first + 1] = std::max(dp[j.first + 1], dp[i] - a + j.second);
	}
	std::cout << dp[n] + a << std::endl;
	
	return 0;
}