#include <bits/stdc++.h>
#define ll long long
#define rep(i,m,n) for(int i=(m); i<=(n); i++)
#define reb(i,m,n) for(int i=(m); i>=(n); i--)
#define pii pair<int,int>
#define pll pair<ll,ll>
#define MP make_pair
#define fs first
#define se second
#define bit(msk, i) ((msk >> i) & 1)
#define iter(id, v) for(auto id : v)
#define pb push_back
#define SZ(v) (int)v.size()
#define ALL(v) v.begin(),v.end()
using namespace std;
mt19937_64 rd(chrono :: steady_clock :: now ().time_since_epoch().count());
ll Rand (ll l, ll r) { return uniform_int_distribution<ll> (l, r) (rd); }
const int N = 1e5 + 7;
const int Mod = 1e9 + 7;
const ll INF = 2e9 + 7;
const ll BASE = 137;
const int szBL = 320;
void inline maximize (ll &A, ll B) { if (A < B) A = B; }
struct Fish {
int fs, se;
ll W;
};
int n, m;
vector<ll> pcur[N], Left[N], Right[N], dp[N], fsuf[N], fpre[N];
vector<pll> high[N];
Fish a[(int)3e5 + 7];
void init (int j, int m) {
pcur[j].resize(m + 2, 0);
Left[j].resize(m + 2, 0);
Right[j].resize(m + 2, 0);
fpre[j].resize(m + 2, 0);
fsuf[j].resize(m + 2, 0);
dp[j].resize(m + 2, 0); ///sửa ik
}
void solution () {
cin >> n >> m;
rep (i, 1, m) {
cin >> a[i].fs >> a[i].se >> a[i].W;
++a[i].fs;
++a[i].se;
high[a[i].fs].pb(MP(a[i].se, a[i].W));
}
high[0] = {MP(0, 0)};
init(0, 5);
rep (j, 1, n) {
iter (&id, high[j - 1]) high[j].pb(MP(id.fs, 0));
iter (&id, high[j + 1]) high[j].pb(MP(id.fs, 0));
high[j].pb(MP(0, 0));
sort (ALL(high[j]));
high[j].resize(unique(ALL(high[j])) - high[j].begin());
int m = SZ(high[j]);
init(j, m);
rep (i, 1, m - 1){
pcur[j][i] = pcur[j][i - 1] + high[j][i].se;
}
rep (i, 1, m - 1) {
int pos = lower_bound(ALL(high[j - 1]), MP(high[j][i].fs, 0LL)) - high[j - 1].begin();
Left[j][i] = pcur[j - 1][pos];
}
}
rep (j, 1, n - 1) {
int m = SZ(high[j]);
rep (i, 1, m - 1) {
int pos = lower_bound(ALL(high[j + 1]), MP(high[j][i].fs, 0LL)) - high[j + 1].begin();
Right[j][i] = pcur[j + 1][pos];
}
}
rep (j, 1, n) {
int m = SZ(high[j]);
vector<pll> &ch = high[j];
dp[j][0] = *max_element(dp[j - 1].begin(), dp[j - 1].end());
if (j == n) {
rep (i, 1, SZ(high[j - 1]) - 1) {
maximize(dp[j][0], dp[j - 1][i] + Right[j - 1][i]);
}
}
if (j == 2) {
rep (i, 1, m - 1) {
dp[j][i] = Left[j][i];
}
}
if (j > 2) {
rep (i, 1, m - 1) {
int pos = upper_bound(ALL(high[j - 2]), MP(ch[i].fs, INF)) - high[j - 2].begin();
maximize(dp[j][i], fpre[j - 2][pos - 1] + Left[j][i]);
maximize(dp[j][i], fsuf[j - 2][pos]);
}
ll premx = 0;
rep (i, 1, SZ(high[j - 1]) - 1) {
premx = max(premx, dp[j - 1][i] - pcur[j - 1][i]);
}
rep (i, 1, m - 1) {
maximize(dp[j][i], Left[j][i] + premx);
}
}
if (j > 3) {
ll premx = 0;
rep (i, 1, SZ(high[j - 3]) - 1) {
premx = max(premx, dp[j - 3][i] + Right[j - 3][i]);
}
rep (i, 1, m - 1) {
maximize(dp[j][i], Left[j][i] + premx);
}
}
fpre[j][0] = dp[j][0];
rep (i, 1, m - 1) {
fpre[j][i] = max(fpre[j][i - 1], dp[j][i]);
}
reb (i, m - 1, 0) {
fsuf[j][i] = max(fsuf[j][i + 1], dp[j][i] + Right[j][i]);
}
// rep (i, 1, m - 1) {
// cout << j << " "<<high[j][i].fs <<" "<< dp[j][i] <<"\n";
// }
}
cout << *max_element(dp[n].begin(), dp[n].end()) <<"\n";
}
#define file(name) freopen(name".inp","r",stdin); \
freopen(name".out","w",stdout);
int main () {
// file("c");
ios_base :: sync_with_stdio(false); cin.tie(0); cout.tie(0);
int num_Test = 1;
// cin >> num_Test;
while (num_Test--)
solution();
}
/*
no bug challenge +2
2 + 8 * 2 - 9
5 4
0 2 5
1 1 2
4 4 1
3 3 3
*/
Compilation message
/usr/bin/ld: /tmp/cc8uozrx.o: in function `main':
grader.cpp:(.text.startup+0x0): multiple definition of `main'; /tmp/ccCCm3Cz.o:fish.cpp:(.text.startup+0x0): first defined here
/usr/bin/ld: /tmp/cc8uozrx.o: in function `main':
grader.cpp:(.text.startup+0x25e): undefined reference to `max_weights(int, int, std::vector<int, std::allocator<int> >, std::vector<int, std::allocator<int> >, std::vector<int, std::allocator<int> >)'
collect2: error: ld returned 1 exit status
