#include <bits/stdc++.h>
using namespace std;
#ifndef LOCAL
#include "fish.h"
#endif
const int N = 300'000 + 10;
int n, m;
struct Fish {
int x, y, w;
} fish[N];
vector<int> pos[N];
vector<long long> h[N];
vector<long long> in[N], de[N];
long long max_weights(int inN, int inM,
vector<int> inX, vector<int> inY, vector<int> inW) {
{ // input
n = inM; m = inN;
for (int i = 1; i <= n; ++i)
fish[i] = {inX[i - 1] + 1, inY[i - 1] + 1, inW[i - 1]};
}
for (int i = 1; i <= n; ++i) {
pos[fish[i].x - 1].push_back(fish[i].y);
pos[fish[i].x].push_back(fish[i].y);
pos[fish[i].x + 1].push_back(fish[i].y);
}
for (int i = 0; i <= m + 1; ++i) {
pos[i].push_back(0);
sort(pos[i].begin(), pos[i].end());
pos[i].erase(unique(pos[i].begin(), pos[i].end()), pos[i].end());
h[i].resize(pos[i].size() + 2);
in[i].resize(pos[i].size() + 2);
de[i].resize(pos[i].size() + 2);
}
for (int i = 1; i <= n; ++i) {
const auto& [x, y, w] = fish[i];
int it = lower_bound(pos[x].begin(), pos[x].end(), y) - pos[x].begin();
h[x][it] = w;
}
for (int i = 1; i <= m; ++i) {
for (int j = 1; j < (int)pos[i].size(); ++j) h[i][j] += h[i][j - 1];
}
for (int i = 1; i <= m; ++i) {
const int sz = pos[i].size() - 1;
{ // calculate sz
if (i > 1) { // start of in
{ // best[<i][j] -> best i j
long long small = 0;
int it1 = 0, it2 = 0, it3 = 0, it4 = 0; // it1 for i - 2, it2 for i - 1, it3 for i - 1 it4 for i + 1
for (int j = 1; j <= sz; ++j) {
auto& ret = in[i][j];
while (it1 < (int)pos[i - 2].size() && pos[i - 2][it1] <= pos[i][j]) {
while (it2 < (int)pos[i - 1].size() && pos[i - 1][it2] <= pos[i - 2][it1]) it2 += 1;
small = max(small, de[i - 2][it1] - h[i - 1][it2 - 1]);
it1 += 1;
}
while (it3 < (int)pos[i - 1].size() && pos[i - 1][it3] <= pos[i][j]) it3 += 1;
while (it4 < (int)pos[i + 1].size() && pos[i + 1][it4] <= pos[i][j]) it4 += 1;
ret = max(ret, h[i - 1][it3 - 1] + small + h[i + 1][it4 - 1]);
}
}
{ // best[>i][j] -> best i j
long long great = 0;
int it1 = pos[i - 2].size() - 1, it2 = pos[i + 1].size() - 1; // it1 for i - 2, it2 for i + 1
for (int j = sz; j >= 1; --j) {
auto& ret = in[i][j];
while (it1 >= 0 && pos[i - 2][it1] >= pos[i][j]) {
great = max(great, de[i - 2][it1]);
it1 -= 1;
}
while (it2 >= 0 && pos[i + 1][it2] > pos[i][j]) it2 -= 1;
ret = max(ret, great + (it2 == -1 ? 0 : h[i + 1][it2]));
}
}
}
{ // pre is in and now is in
long long ma = 0;
int it1 = 0, it2 = 0; //it1 for i - 1, it2 for i + 1;
for (int j = 1; j <= sz; ++j) {
auto& ret = in[i][j];
while (it1 < (int)pos[i - 1].size() && pos[i - 1][it1] <= pos[i][j]) {
if (i == 3 && j == 1) {
// cerr << pos[i - 1][it1] << " " << in[i - 1][it1] << " " << h[i - 1][it1] << " " << h[i][j] << "\n";
// cerr << in[i - 1][it1] << "\n";
}
ma = max(ma, in[i - 1][it1] - h[i - 1][it1] - h[i][j]);
it1 += 1;
}
while (it2 < (int)pos[i + 1].size() && pos[i + 1][it2] <= pos[i][j]) it2 += 1;
if (i == 3 && j == 1) {
// cerr << ma << "\n";
// cerr << it1 << " " << h[i - 1][it1] << "\n";
}
ret = max(ret, h[i - 1][it1 - 1] + ma + h[i + 1][it2 - 1]);
}
}
}
{ // calculate de
long long ma = 0;
int it1 = pos[i - 1].size() - 1, it2 = pos[i + 1].size() - 1; // it1 for i + 1, it2 for i + 1;
for (int j = sz; j >= 1; --j) {
auto& ret = de[i][j];
while (it1 >= 0 && pos[i - 1][it1] >= pos[i][j]) {
ma = max(ma, de[i - 1][it1]);
it1 -= 1;
}
while (it2 >= 0 && pos[i + 1][it2] > pos[i][j]) it2 -= 1;
ret = max({ret, ma - h[i][j] + (it2 == -1 ? 0 : h[i + 1][it2]), in[i][j]});
}
for (int j = 0; j < (int)pos[i - 1].size(); ++j) de[i][0] = max(de[i][0], de[i - 1][j]);
}
}
return *max_element(de[m].begin(), de[m].end());
}
#ifdef LOCAL
int main() {
int N, M;
assert(2 == scanf("%d %d", &N, &M));
std::vector<int> X(M), Y(M), W(M);
for (int i = 0; i < M; ++i) {
assert(3 == scanf("%d %d %d", &X[i], &Y[i], &W[i]));
}
long long result = max_weights(N, M, X, Y, W);
printf("%lld\n", result);
return 0;
}
#endif
