#include <bits/stdc++.h>
using namespace std;
using ii = pair<int, int>;
const int32_t N = 1e5 + 5,
M = 3e5 + 5;
const int64_t INF = 1e18;
int n, m;
struct info{
int x, y, w;
info(){}
info(int x, int y, int w): x(x), y(y), w(w) {}
} fish[M];
namespace AC{
vector<ii> fish_in_col[N];
vector<long long> pref[2][N], dp[2][N];
long long _max[N];
void init(){
for(int i = 1; i <= m; i++) fish_in_col[fish[i].x].emplace_back(fish[i].y, fish[i].w);
for(int i = 1; i <= n; i++){
fish_in_col[i].emplace_back(0, 0);
sort(fish_in_col[i].begin(), fish_in_col[i].end());
for(auto x : {0, 1}) dp[x][i].resize(fish_in_col[i].size() + 1, 0);
//
_max[i] = -INF;
pref[1][i].resize(fish_in_col[i].size() + 1, (i > 1 ? -INF : 0));
pref[0][i].resize(fish_in_col[i].size() + 1, (i > 1 ? -INF : 0));
}
}
int solve(){
init();
long long res = 0;
for(int i = 1; i <= n; i++){
if(i > 1){
long long add = 0, sub = 0;
for(int j = 1, pj = 0; j < fish_in_col[i].size(); j++){
auto [y, w] = fish_in_col[i][j];
add += w;
while(pj < fish_in_col[i - 1].size() - 1 && fish_in_col[i - 1][pj + 1].first < fish_in_col[i][j].first) sub += fish_in_col[i - 1][++pj].second;
auto tmp = (fish_in_col[i - 1][pj].first < fish_in_col[i][j].first);
dp[0][i][j] = max(dp[0][i][j], pref[0][i - 1][pj + tmp] + add - sub);
// cout << i << " " << y << " " << dp[0][i][j] << "\n";
}
for(int j = 1; j < fish_in_col[i - 2].size(); j++) dp[0][i][fish_in_col[i].size()-1] = max({dp[0][i][fish_in_col[i].size()-1], dp[0][i - 2][j] + add, dp[1][i - 2][j] + add});
}
if(i < n){
long long add = 0;
for(int j = 1; j < fish_in_col[i].size(); j++){
auto [y, w] = fish_in_col[i][j];
add += w;
dp[1][i][j] = max(dp[1][i][j], pref[1][i][j] + add);
dp[1][i][j] = max(dp[1][i][j], (i > 1 ? pref[0][i - 1][0] : 0) + add);
if(i > 1) dp[1][i][j] = max(dp[1][i][j], _max[i - 2]);
}
res = max(res, dp[1][i][fish_in_col[i].size() - 1]);
}
for(int j = fish_in_col[i].size() - 1; j >= 0; j--){
pref[0][i][j] = max(dp[0][i][j], pref[0][i][j + 1]);
_max[i] = max(_max[i], dp[1][i][j]);
}
long long add = 0;
for(int j = 1; j < fish_in_col[i + 1].size(); j++){
auto [y, w] = fish_in_col[i + 1][j];
add += w;
int pj = upper_bound(fish_in_col[i].begin(), fish_in_col[i].end(), make_pair(y, -1)) - fish_in_col[i].begin() - 1;
pref[1][i + 1][j] = max(pref[1][i + 1][j - 1], dp[1][i][pj] - add);
}
res = max(res, pref[0][i][0]);
}
return res;
}
}
int64_t max_weights(int _N, int _M, vector<int> _X, vector<int> _Y, vector<int> _W){
n = _N; m = _M;
for(int i = 0; i < m; i++) fish[i + 1] = info(_X[i] + 1, _Y[i] + 1, _W[i]);
bool flag1 = true;
for(int i = 1; i <= m; i++) if(!(fish[i].x & 1)){ flag1 = false; break; }
return AC::solve();
}
//#define zNatsumi
#ifdef zNatsumi
int main(){
cin.tie(0)->sync_with_stdio(0);
#define task "test"
if(fopen(task ".inp", "r")){
freopen(task ".inp", "r", stdin);
freopen(task ".out", "w", stdout);
}
int n, m; cin >> n >> m;
vector<int> x(m), y(m), w(m);
for(int i = 0; i < m; i++) cin >> x[i] >> y[i] >> w[i];
cout << max_weights(n, m, x, y, w);
}
/*
5 4
0 2 5
1 1 2
4 4 1
3 3 3
*/
#endif
