#include <iostream>
#include <vector>

template <class T>
std::vector<T> vec(int len, T elem) { return std::vector<T>(len, elem); }

using lint = long long;
constexpr lint INF = 1LL << 60;

void solve() {
    int n, m;
    lint a;
    std::cin >> n >> m >> a;

    std::vector<std::vector<std::pair<int, lint>>> rs(n);
    while (m--) {
        int l, r;
        lint p;
        std::cin >> l >> r >> p;
        --l, --r;
        rs[l].emplace_back(r, p);
    }

    auto dp = vec(2, vec(n + 1, -INF));
    dp[1][0] = 0;
    for (int l = 0; l < n; ++l) {
        for (auto [r, p] : rs[l]) {
            for (int i = 0; i < 2; ++i) {
                dp[1][r + 1] = std::max(dp[1][r + 1],
                                        dp[i][l] + p - a * (2 - i));
            }
        }

        for (int i = 0; i < 2; ++i) {
            dp[0][l + 1] = std::max(dp[0][l + 1], dp[i][l]);
        }
    }

    std::cout << std::max(dp[0][n], dp[1][n] + a) << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}