#include <bits/stdc++.h>
using namespace std;

struct iofast_t {
    iofast_t() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr); cout.tie(nullptr);
    }
} iofast;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return std::vector(arg, init);
    else return std::vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

int main() {
    int n, m, a; cin >> n >> m >> a;
    auto range = vec<tuple<int, int>>(uns, n + 1, 0);
    for (int i = 0; i < m; ++i) {
        int l, r, p; cin >> l >> r >> p;
        range[r].emplace_back(l, p);
    }

    auto dp = vec<int64_t>(0, n + 1, 2);
    for (int i = 1; i <= n; ++i) {
        dp[i][0] = max(dp[i - 1][0], dp[i - 1][1]);
        dp[i][1] = max(dp[i - 1][0], dp[i - 1][1]) + -a * (i != n);
        for (auto [l, p] : range[i]) {
            dp[i][1] = max({
                dp[i][1],
                dp[l - 1][1] + p - a * (i != n),
                dp[l - 1][0] + p - a * (l - 1 != 0) - a * (i != n),
            });
        }
    }

    cout << dp[n][1] << endl;
}