#include <bits/stdc++.h>
#pragma GCC diagnostic ignored "-Wsign-compare"
#pragma GCC diagnostic ignored "-Wsign-conversion"
#define NDEBUG
#define SHOW(...) static_cast<void>(0)
//!===========================================================!//
//!  dP     dP                          dP                    !//
//!  88     88                          88                    !//
//!  88aaaaa88a .d8888b. .d8888b. .d888b88 .d8888b. 88d888b.  !//
//!  88     88  88ooood8 88'  '88 88'  '88 88ooood8 88'  '88  !//
//!  88     88  88.  ... 88.  .88 88.  .88 88.  ... 88        !//
//!  dP     dP  '88888P' '88888P8 '88888P8 '88888P' dP        !//
//!===========================================================!//
template <typename T>
T read()
{
    T v;
    return std::cin >> v, v;
}
template <typename T>
std::vector<T> readVec(const std::size_t l)
{
    std::vector<T> v(l);
    for (auto& e : v) { std::cin >> e; }
    return v;
}
using ld = long double;
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
constexpr unsigned int MOD = 1000000007;
template <typename T>
constexpr T INF = std::numeric_limits<T>::max() / 4;
template <typename F>
constexpr F PI = static_cast<F>(3.1415926535897932385);
std::mt19937 mt{std::random_device{}()};
template <typename T>
bool chmin(T& a, const T& b) { return (a > b ? a = b, true : false); }
template <typename T>
bool chmax(T& a, const T& b) { return (a < b ? a = b, true : false); }
template <typename T>
std::vector<T> Vec(const std::size_t n, T v) { return std::vector<T>(n, v); }
template <class... Args>
auto Vec(const std::size_t n, Args... args) { return std::vector<decltype(Vec(args...))>(n, Vec(args...)); }
template <typename T>
constexpr T popCount(const T u)
{
#ifdef __has_builtin
    return u == 0 ? T(0) : (T)__builtin_popcountll(u);
#else
    unsigned long long v = static_cast<unsigned long long>(u);
    return v = (v & 0x5555555555555555ULL) + (v >> 1 & 0x5555555555555555ULL), v = (v & 0x3333333333333333ULL) + (v >> 2 & 0x3333333333333333ULL), v = (v + (v >> 4)) & 0x0F0F0F0F0F0F0F0FULL, static_cast<T>(v * 0x0101010101010101ULL >> 56 & 0x7f);
#endif
}
template <typename T>
constexpr T log2p1(const T u)
{
#ifdef __has_builtin
    return u == 0 ? T(0) : T(64 - __builtin_clzll(u));
#else
    unsigned long long v = static_cast<unsigned long long>(u);
    return v = static_cast<unsigned long long>(v), v |= (v >> 1), v |= (v >> 2), v |= (v >> 4), v |= (v >> 8), v |= (v >> 16), v |= (v >> 32), popCount(v);
#endif
}
template <typename T>
constexpr T clog(const T v) { return v == 0 ? T(0) : log2p1(v - 1); }
template <typename T>
constexpr T msbp1(const T v) { return log2p1(v); }
template <typename T>
constexpr T lsbp1(const T v)
{
#ifdef __has_builtin
    return __builtin_ffsll(v);
#else
    return v == 0 ? T(0) : popCount((v & (-v)) - T(1)) + T(1);
#endif
}
template <typename T>
constexpr bool ispow2(const T v) { return popCount(v) == 1; }
template <typename T>
constexpr T ceil2(const T v) { return v == 0 ? T(1) : T(1) << log2p1(v - 1); }
template <typename T>
constexpr T floor2(const T v) { return v == 0 ? T(0) : T(1) << (log2p1(v) - 1); }
//!===================================================================!//
//!  .d88888b                    d888888P                             !//
//!  88.    "'                      88                                !//
//!  'Y88888b. .d8888b. .d8888b.    88    88d888b. .d8888b. .d8888b.  !//
//!        '8b 88ooood8 88'  '88    88    88'  '88 88ooood8 88ooood8  !//
//!  d8'   .8P 88.  ... 88.  .88    88    88       88.  ... 88.  ...  !//
//!   Y88888P  '88888P' '8888P88    dP    dP       '88888P' '88888P'  !//
//!                          .88                                      !//
//!                      d8888P                                       !//
//!===================================================================!//
template <typename ValMonoid>
class SegTree
{
public:
    using ValType = typename ValMonoid::ValType;
    SegTree(const std::size_t N, const ValType initial = ValMonoid::id()) : size(N), half(ceil2(size)), val(half << 1, ValMonoid::id())
    {
        if (initial != ValMonoid::id()) {
            std::fill(val.begin() + half, val.end(), initial);
            for (std::size_t i = half - 1; i >= 1; i--) { up(i); }
        }
    }
    template <typename InIt>
    SegTree(const InIt first, const InIt last) : size(std::distance(first, last)), half(ceil2(size)), val(half << 1, ValMonoid::id())
    {
        std::copy(first, last, val.begin() + half);
        for (std::size_t i = half - 1; i >= 1; i--) { up(i); }
    }
    ValType get(const std::size_t a) const { return assert(a < size), val[a + half]; }
    void set(std::size_t a, const ValType& v)
    {
        assert(a < size);
        val[a += half] = v;
        while (a >>= 1) { up(a); }
    }
    ValType fold(std::size_t L, std::size_t R) const
    {
        assert(L < R), assert(R <= size);
        ValType accl = ValMonoid::id(), accr = ValMonoid::id();
        for (L += half, R += half; L < R; L >>= 1, R >>= 1) {
            if (L & 1) { accl = acc(accl, val[L++]); }
            if (R & 1) { accr = acc(val[--R], accr); }
        }
        return acc(accl, accr);
    }
    friend std::ostream& operator<<(std::ostream& os, const SegTree& seg)
    {
        os << "[";
        for (std::size_t i = seg.half; i < seg.half + seg.size; i++) { os << seg.val[i] << (i + 1 == seg.half + seg.size ? "" : ","); }
        return (os << "]\n");
    }

private:
    void up(const std::size_t i) { val[i] = acc(val[i << 1], val[i << 1 | 1]); }
    const std::size_t size, half;
    std::vector<ValType> val;
    const ValMonoid acc{};
};
//!==================================!//
//!  8888ba.88ba                     !//
//!  88  '8b  '8b                    !//
//!  88   88   88 .d8888b. dP.  .dP  !//
//!  88   88   88 88'  '88  '8bd8'   !//
//!  dP   dP   dP '88888P8 dP'  'dP  !//
//!==================================!//
template <typename ElemType>
struct Max
{
    using ValType = ElemType;
    ValType operator()(const ValType& a, const ValType& b) const { return std::max(a, b); }
    static constexpr ValType id() { return std::numeric_limits<ValType>::min(); }
};
int main()
{
    const int N = read<int>(), M = read<int>();
    const ll A = read<ll>();
    std::vector<int> L(M), R(M);
    std::vector<ll> P(M);
    for (int i = 0; i < M; i++) { std::cin >> L[i] >> R[i] >> P[i]; }
    std::vector<int> ind(M);
    std::iota(ind.begin(), ind.end(), 0);
    std::sort(ind.begin(), ind.end(), [&](const int i, const int j) { return R[i] == R[j] ? L[i] < L[j] : R[i] < R[j]; });
    SegTree<Max<ll>> dp(N + 1, -INF<ll>);
    dp.set(0, A);
    for (const int i : ind) {
        const int l = L[i], r = R[i];
        ll max = std::max(dp.get(l - 1) - A, (l == 1 ? 0 : dp.fold(0, l - 1)) - 2 * A);
        dp.set(r, std::max(dp.get(r), max + P[i]));
    }
    std::cout << std::max({dp.fold(0, N) - A, dp.get(N)}) << std::endl;
    return 0;
}