#include<bits/stdc++.h>
using namespace std;
const int N=110;
int vis[N];
int hate[N];
int v[N];
int n;
int mx=-1;
void dfs(int val,int now)
{
//	cout<<now<<" "<<val<<endl;
	bool cannxt=false;
	vis[now]=1;vis[hate[now]]=1;
	for(int i=1;i<=n;i++)
	{
		if(!vis[i]&&!vis[hate[i]])
		{
			cannxt=true;
			dfs(val+v[i],i);
		}
	}
	vis[now]=0;vis[hate[now]]=0;
	if(!cannxt)
	{
		mx=max(mx,val);
	}
	return;
}
int main()
{
	freopen("bzoj_1040.in","r",stdin);
	freopen("bzoj_1040.out","w",stdout);
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>v[i]>>hate[i];
	}
	dfs(0,0);
	cout<<mx;
}