#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];
namespace sub6 {
const int SZ = 3000 + 10;
long long w[SZ][SZ], h[SZ][SZ];
long long inc[SZ][SZ], dec[SZ][SZ], best[SZ][SZ];
bool checkCondition() { return m <= 3000; }
long long solve() {
for (int i = 1; i <= n; ++i) w[fish[i].x][fish[i].y] = fish[i].w;
for (int i = 1; i <= m; ++i) {
for (int j = 1; j <= m; ++j) h[i][j] = h[i - 1][j] + w[i][j];
}
for (int j = 1; j <= m; ++j) {
{ // calculate inc
if (j > 1) { // start of inc
{ // best[<i][j] -> best i j
long long ma = 0;
for (int i = 1; i <= m; ++i) {
auto& ret = inc[i][j];
ma = max(ma, best[i - 1][j - 2] - h[i - 1][j - 1]);
ret = max(ret, ma + h[i][j + 1] + h[i][j - 1]);
}
}
{ // best[>i][j] -> best i j
long long ma = 0;
for (int i = m; i >= 1; --i) {
auto& ret = inc[i][j];
ma = max(ma, best[i][j - 2]);
ret = max(ret, ma + h[i][j + 1]);
}
}
}
{ // pre is inc and now is inc
long long ma = 0;
for (int i = 1; i <= m; ++i) {
auto& ret = inc[i][j];
ma = max(ma, inc[i][j - 1] - h[i][j - 1] - h[i][j]);
ret = max(ret, ma + h[i][j - 1] + h[i][j + 1]);
}
}
}
{ // calculate dec
{ // from inc to deg :)
for (int i = 1; i <= m; ++i) dec[i][j] = inc[i][j];
}
{ // pre is dec and now is dec
long long ma = 0;
for (int i = m; i >= 1; --i) {
auto& ret = dec[i][j];
ma = max(ma, dec[i][j - 1]);
ret = max(ret, ma - h[i][j] + h[i][j + 1]);
}
}
}
{ // calculate f
for (int i = 0; i <= m; ++i) {
best[i][j] = max({best[i][j], inc[i][j], dec[i][j]});
best[0][j] = max(best[0][j], best[i][j - 1]);
}
}
}
long long answer = 0;
for (int i = 0; i <= m; ++i) answer = max(answer, best[i][m]);
return answer;
}
}
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] = {inY[i - 1] + 1, inX[i - 1] + 1, inW[i - 1]};
}
if (sub6::checkCondition()) return sub6::solve();
return 0;
}
#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
