#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using P = pair<int, ll>;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n, m;
    ll a;
    cin >> n >> m >> a;
    vector< vector<P> > v(n + 1);
    for (int i = 0; i < m; i++) {
        int l, r;
        ll p;
        cin >> l >> r >> p;
        l--;
        v[r].emplace_back(l, p);
    }

    vector<ll> dp(n + 1, 0);
    ll sum = 0;
    for (int i = 1; i <= n; i++) {
        dp[i] = sum;
        for (P& p : v[i]) {
            dp[i] = max(dp[i], dp[p.first] + p.second);
        }
        if (i < n) dp[i] -= a;
        sum = max(sum, dp[i]);
    }
    cout << dp[n] << endl;
    return 0;
}