#include <vector>
#include <map>
#include <iostream>
using namespace std;
int main() {
    int n, m, a; cin >> n >> m >> a;
    map<int, vector<pair<int, int> > > mp;
    for (int i = 0; i < m; i++) {
        int l, r, p; cin >> l >> r >> p;
        mp[r].push_back({l, p});
    }
    long long dp[n+1], acc[n+1];
    dp[0] = acc[0] = 0;
    for (int x = 1; x <= n; x++) {
        long long val = -(1LL<<60);
        int cost = x == n ? 0 : a;
        for (auto interval : mp[x]) {
            int l = interval.first, p = interval.second;
            val = max(val, acc[l-1] + p - cost - a);
            val = max(val, dp[l-1] + p - cost);
        }
        dp[x] = val;
        acc[x] = max(acc[x-1], dp[x]);
        // cerr << x << ' ' << dp[x] << ' ' << acc[x] << endl;
    }
    cout << acc[n] << endl;
}