// need
#include <iostream>
#include <algorithm>
// data structure
#include <bitset>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <complex>
//#include <deque>
#include <valarray>
#include <unordered_map>
#include <unordered_set>
#include <array>
// stream
//#include <istream>
#include <sstream>
//#include <ostream>
#include <fstream>
// etc
#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
//#include <chrono>
#include <random>
#include <numeric>

// input
#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__);
template<typename T> void MACRO_VAR_Scan(T& t) { std::cin >> t; }
template<typename First, typename...Rest>void MACRO_VAR_Scan(First& first, Rest&...rest) { std::cin >> first; MACRO_VAR_Scan(rest...); }
#define VEC_ROW(type, n, ...)std::vector<type> __VA_ARGS__;MACRO_VEC_ROW_Init(n, __VA_ARGS__); for(int w_=0; w_<n; ++w_){MACRO_VEC_ROW_Scan(w_, __VA_ARGS__);}
template<typename T> void MACRO_VEC_ROW_Init(int n, T& t) { t.resize(n); }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Init(int n, First& first, Rest&...rest) { first.resize(n); MACRO_VEC_ROW_Init(n, rest...); }
template<typename T> void MACRO_VEC_ROW_Scan(int p, T& t) { std::cin >> t[p]; }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Scan(int p, First& first, Rest&...rest) { std::cin >> first[p]; MACRO_VEC_ROW_Scan(p, rest...); }
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& R:c)for(auto& w:R)std::cin>>w;
// output
#define OUT(dist) std::cout<<(dist);
#define FOUT(n, dist) std::cout<<std::fixed<<std::setprecision(n)<<(dist);
#define SOUT(n, c, dist) std::cout<<std::setw(n)<<std::setfill(c)<<(dist);
#define SP std::cout<<" ";
#define TAB std::cout<<"\t";
#define BR std::cout<<"\n";
#define SPBR(w, n) std::cout<<(w + 1 == n ? '\n' : ' ');
#define ENDL std::cout<<std::endl;
#define FLUSH std::cout<<std::flush;
#define SHOW(dist) {std::cerr << #dist << "\t:" << (dist) << "\n";}
#define SHOWVECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOWVECTOR2(v) {std::cerr << #v << "\t:\n";for(const auto& xxx : v){for(const auto& yyy : xxx){std::cerr << yyy << " ";}std::cerr << "\n";}}
#define SHOWQUEUE(a) {auto tmp(a);std::cerr << #a << "\t:";while(!tmp.empty()){std::cerr << tmp.front() << " ";tmp.pop();}std::cerr << "\n";}
// utility
#define ALL(a) (a).begin(),(a).end()
#define FOR(w, a, n) for(int w=(a);w<(n);++w)
#define RFOR(w, a, n) for(int w=(n)-1;w>=(a);--w)
#define REP(w, n) for(int w=0;w<int(n);++w)
#define RREP(w, n) for(int w=int(n)-1;w>=0;--w)
#define FORLL(w, a, n) for(ll w=ll(a);w<ll(n);++w)
#define RFORLL(w, a, n) for(ll w=ll(n)-1;w>=ll(a);--w)
#define REPLL(w, n) for(ll w=0;w<ll(n);++w)
#define RREPLL(w, n) for(ll w=ll(n)-1;w>=0;--w)
#define IN(a, x, b) (a<=x && x<b)
template<class T> inline T CHMAX(T& a, const T b) { return a = (a < b) ? b : a; }
template<class T> inline T CHMIN(T& a, const T b) { return a = (a > b) ? b : a; }
#define EXCEPTION(msg) throw std::string("Exception : " msg " [ in ") + __func__ + " : " + std::to_string(__LINE__) + " lines ]"
#define TRY(cond, msg) try {if (cond) EXCEPTION(msg);}catch (std::string s) {std::cerr << s << std::endl;}
//void CHECKTIME(std::function<void()> f) { auto start = std::chrono::system_clock::now(); f(); auto end = std::chrono::system_clock::now(); auto res = std::chrono::duration_cast<std::chrono::nanoseconds>((end - start)).count(); std::cerr << "[Time:" << res << "ns  (" << res / (1.0e9) << "s)]\n"; }
// test
template<class T> std::vector<std::vector<T>> VV(int n, int m, T init = T()) {
	return std::vector<std::vector<T>>(n, std::vector<T>(m, init));
}
template<typename S, typename T>
std::ostream& operator<<(std::ostream& os, std::pair<S, T> p) {
	os << "(" << p.first << ", " << p.second << ")"; return os;
}

// type/const
#define int ll
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using PAIR = std::pair<int, int>;
using PAIRLL = std::pair<ll, ll>;
constexpr int INFINT = 1 << 30;                          // 1.07x10^ 9
constexpr int INFINT_LIM = (1LL << 31) - 1;              // 2.15x10^ 9
constexpr ll INFLL = 1LL << 60;                          // 1.15x10^18
constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);  // 9.22x10^18
constexpr double EPS = 1e-10;
constexpr int MOD = 1000000007;
constexpr double PI = 3.141592653589793238462643383279;
template<class T, size_t N> void FILL(T(&a)[N], const T& val) { for (auto& x : a) x = val; }
template<class ARY, size_t N, size_t M, class T> void FILL(ARY(&a)[N][M], const T& val) { for (auto& b : a) FILL(b, val); }
template<class T> void FILL(std::vector<T>& a, const T& val) { for (auto& x : a) x = val; }
template<class ARY, class T> void FILL(std::vector<std::vector<ARY>>& a, const T& val) { for (auto& b : a) FILL(b, val); }
// ------------>8------------------------------------->8------------

// ------------>8---------- LazySegmentTree ---------->8------------

// ## write [ LST lst(n, SUM/MAX/MIN, ADD/UPD) ] when using this snippet.
enum QUERY_SEG_LazySegmentTree { SUM, MAX, MIN };
enum QUERY_LAZ_LazySegmentTree { ADD, UPD };
template<class SEG, class LAZ>
class LazySegmentTree {
private:
	std::vector<SEG> seg;
	std::vector<LAZ> laz;
	std::vector<bool> isUpdated;
	int ARY_SIZE;
	SEG eSeg;
	LAZ eLaz;
	std::function<SEG(SEG&, SEG&)> mergeSeg;
	std::function<LAZ(LAZ&, LAZ&)> mergeLaz;
	std::function<SEG(SEG&, LAZ&, int)> applyLaz;

	void push(int k, int l, int r) {
		if (!isUpdated[k]) {
			applyLaz(seg[k], laz[k], r - l);
			if (r - l > 1) {
				mergeLaz(laz[k * 2 + 1], laz[k]); isUpdated[k * 2 + 1] = false;
				mergeLaz(laz[k * 2 + 2], laz[k]); isUpdated[k * 2 + 2] = false;
			}
			isUpdated[k] = true;
			laz[k] = eLaz;
		}
	}
public:
	LazySegmentTree(int n, QUERY_SEG_LazySegmentTree qSeg, QUERY_LAZ_LazySegmentTree qLaz) : ARY_SIZE(1) {
		ARY_SIZE = 1;
		while (ARY_SIZE < n) ARY_SIZE *= 2;
		seg.resize(ARY_SIZE * 2 - 1);
		laz.resize(ARY_SIZE * 2 - 1);
		isUpdated.resize(ARY_SIZE * 2 - 1, true);

		switch (qSeg) {
		case SUM:
			eSeg = 0;
			mergeSeg = [](SEG& l, SEG& r) { return l + r; };
			break;
		case MAX:
			eSeg = std::numeric_limits<SEG>::lowest();
			mergeSeg = [](SEG& l, SEG& r) { return std::max(l, r); };
			break;
		case MIN:
			eSeg = std::numeric_limits<SEG>::max();
			mergeSeg = [](SEG& l, SEG& r) { return std::min(l, r); };
			break;
		default:
			struct INVALID_QUERY_TYPE_ERROR {};
			throw INVALID_QUERY_TYPE_ERROR();
			break;
		}

		switch (qLaz)
		{
		case ADD:
			eLaz = 0;
			mergeLaz = [](LAZ& l, LAZ& r) { return l += r; };
			if (qSeg == SUM) applyLaz = [](SEG& s, LAZ& l, int w) { return s += l * w; };
			else applyLaz = [](SEG& s, LAZ& l, int w) { return s += l; };
			break;
		case UPD:
			eLaz = 0;
			mergeLaz = [](LAZ& l, LAZ& r) { return l = r; };
			if (qSeg == SUM) applyLaz = [](SEG& s, LAZ& l, int w) { return s = l * w; };
			else applyLaz = [](SEG& s, LAZ& l, int w) { return s = l; };
			break;
		default:
			struct INVALID_QUERY_TYPE_ERROR {};
			throw INVALID_QUERY_TYPE_ERROR();
			break;
		}
	}
	void update(int a, int b, SEG v, int k, int l, int r) {
		push(k, l, r);
		if (r <= a || b <= l) return;
		if (a <= l && r <= b) {
			LAZ la(v);
			mergeLaz(laz[k], la);
			isUpdated[k] = false;
			push(k, l, r);
		}
		else {
			update(a, b, v, k * 2 + 1, l, (l + r) / 2);
			update(a, b, v, k * 2 + 2, (l + r) / 2, r);
			seg[k] = mergeSeg(seg[k * 2 + 1], seg[k * 2 + 2]);
		}
	}
	// ## update [l, r) with v
	void update(int l, int r, SEG v) {
		update(l, r, v, 0, 0, ARY_SIZE);
	}
	SEG query(int a, int b, int k, int l, int r) {
		push(k, l, r);
		if (r <= a || b <= l) return eSeg;
		if (a <= l && r <= b) return seg[k];
		SEG vl = query(a, b, k * 2 + 1, l, (l + r) / 2);
		SEG vr = query(a, b, k * 2 + 2, (l + r) / 2, r);
		return mergeSeg(vl, vr);
	}
	// ## return SUM/MAX/MIN in [l, r)
	SEG query(int l, int r) {
		return query(l, r, 0, 0, ARY_SIZE);
	}
};

using LST = LazySegmentTree<ll, ll>;
// ------------>8---------- LazySegmentTree ---------->8------------


signed main() {
	INIT;

	VAR(int, n, m);
	VEC_ROW(int, m, l, r, a);

	std::vector<std::vector<int>> L(n + 1), R(n + 1);
	REP(i, m) {
		--l[i]; --r[i];
		L[l[i]].emplace_back(i);
		R[r[i]].emplace_back(i);
	}

	LST dp(n + 1, MAX, ADD);
	dp.update(0, 1, 0);

	REP(i, n) {
		for (auto& pl : L[i]) {
			dp.update(0, l[pl] + 1, a[pl]);
		}

		dp.update(i + 1, i + 2, dp.query(0, i + 1));

		for (auto& pr : R[i]) {
			dp.update(0, l[pr] + 1, -a[pr]);
		}
	}
	OUT(dp.query(0, n + 1))BR;
	return 0;
}

Measured memory_bytes: 35072