10pts AC#2#9求条

#include<bits/stdc++.h>
#define int long long
#define lft(x) (x==0?h.size()-1:x-1)
#define rht(x) (x==h.size()-1?0:x+1)
#define _w(x) (x>=ow_?x-ow_:x)
using namespace std;
int n,ans,land_max,dist[1000005],sum[1000005];
bool vis[1000005],flag;
struct node{int v,w,b;};
vector<node> vct[1000005];
vector<int> h,w_;
stack<int> stk;
deque<int> q;
void find_huan(int u,int fb){
	vis[u]=1;
	stk.push(u);
	for(int i=0;i<vct[u].size();i++){
		int v=vct[u][i].v,b=vct[u][i].b;
		if(abs(b-fb)==n)continue;
		if(vis[v]&&!flag){
			while(stk.top()!=v){
				h.push_back(stk.top());
				stk.pop();
			}
			h.push_back(v);
			stk.pop();
			flag=1;
			continue;
		}
		if(vis[v])continue;
		find_huan(v,b);
	}
	if(!flag)stk.pop();
}
void tree_long(int u,int f,int k){
	for(int i=0;i<vct[u].size();i++){
		int v=vct[u][i].v,w=vct[u][i].w;
		if(v==f||v==h[lft(k)]||v==h[rht(k)])continue;
		tree_long(v,u,k);
		land_max=max(land_max,dist[u]+dist[v]+w);
		dist[u]=max(dist[u],dist[v]+w);
	}
}
void go_round(int u,int en,bool flag){
	if(u==en&&flag)return;
	for(int i=0;i<vct[h[u]].size();i++){
		if(vct[h[u]][i].v==h[rht(u)]){
			go_round(rht(u),en,1);
			w_.push_back(vct[h[u]][i].w);
			break;
		}
	}
}
int solve_land(int root){
	h.clear();
	flag=land_max=0;
	while(stk.size())stk.pop();
	find_huan(root,-2e9);
	for(int i=0;i<h.size();i++){
		tree_long(h[i],-1,i);
	}
	if(h.size()==2){
		for(int i=0;i<vct[h[0]].size();i++){
			if(vct[h[0]][i].v==h[lft(0)])land_max=max(land_max,dist[h[0]]+dist[h[1]]+vct[h[0]][i].w);
		}
	}else{
		w_.clear();
		go_round(0,0,0);
		int ow_=w_.size();
		for(int i=0;i<w_.size()/2;i++){
			swap(w_[i],w_[w_.size()-i-1]);
		}
		for(int i=0;i<ow_;i++){
			w_.push_back(w_[i]);
		}
		w_.pop_back();
		sum[0]=w_[0];
		for(int i=1;i<w_.size();i++){
			sum[i]=sum[i-1]+w_[i];
		}
		while(q.size())q.pop_front();
		int last=0;
		q.push_back(dist[h[0]]);
		for(int i=1;i<w_.size();i++){
			if(i-last!=ow_)land_max=max(land_max,dist[h[_w(i)]]+sum[i-1]+q.front());
			while(q.size()&&q.back()<dist[h[_w(i)]]-sum[i-1])q.pop_back();
			if(q.empty())last=i;
			q.push_back(dist[h[_w(i)]]-sum[i-1]);
		}
	}
	return land_max;
}
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cin>>n;
	for(int i=1;i<=n;i++){
		int v,w;
		cin>>v>>w;
		vct[v].push_back({i,w,i});
		vct[i].push_back({v,w,n+i});
	}
	for(int i=1;i<=n;i++){
		if(vis[i])continue;
		ans+=solve_land(i);
	}
	cout<<ans;
	return 0;
}