#include <bits/stdc++.h>
#define pb push_back
#define fst first
#define snd second
#define fore(i,a,b) for(int i=a,pao=b;i<pao;++i)
#define SZ(x) ((int)x.size())
#define ALL(x) x.begin(),x.end()
#define mset(a,v) memset((a),(v),sizeof(a))
#define FIN ios::sync_with_stdio(0);cin.tie(0);cout.tie(0)
using namespace std;
typedef long long ll;
const int MAXN=1e5+5;
const ll INF=1e18;
int n;
vector<pair<int,int>>s[MAXN];
ll best[MAXN];
struct STree{
ll st[MAXN*4];
void init(){
fore(i,0,MAXN*4)st[i]=-INF;
}
void upd(int p,ll x,int v=1,int s=0,int e=n+1){
if(s==e){
st[v]=max(st[v],x);
return;
}
int m=(s+e)/2;
if(p<=m)upd(p,x,v*2,s,m);
else upd(p,x,v*2+1,m+1,e);
st[v]=max(st[v*2],st[v*2+1]);
}
ll que(int ts,int te,int v=1,int s=0,int e=n+1){
if(e<ts||te<s)return -INF;
if(ts<=s&&e<=te)return st[v];
int m=(s+e)/2;
return max(que(ts,te,v*2,s,m),que(ts,te,v*2+1,m+1,e));
}
ll get(){
return que(0,n+1);
}
}inc,decs; //uno para los pilares crecientes y decrecientes
long long max_weights(int N, int M, std::vector<int> X, std::vector<int> Y, std::vector<int> W) {
n=N;
fore(i,0,M){
s[X[i]].pb({Y[i],W[i]});
sort(ALL(s[X[i]]));
}
inc.init();
decs.init();
inc.upd(0,0);
fore(i,0,n-1){
ll ant=decs.get();
decs.upd(n,inc.get());
for(auto&[p,w]:s[i]){
inc.upd(p+1,w+inc.que(0,p));
}
inc.upd(0,best[i]);
reverse(ALL(s[i+1]));
for(auto&[p,w]:s[i+1]){
ll val=w+decs.que(p+1,n);
best[i+1]=max(best[i+1],val);
decs.upd(p,val);
}
inc.upd(0,ant);
reverse(ALL(s[i+1]));
//~ cout<<endl;
//~ fore(j,0,n+1){
//~ cout<<inc.que(j,j)<<" ";
//~ }
//~ cout<<endl;
//~ fore(j,0,n+1){
//~ cout<<decs.que(j,j)<<" ";
//~ }
//~ cout<<endl;
}
return max(inc.get(),decs.get());
}
