#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
const int M = 200005;
#define int long long
#define pii pair<int,int>
#define pb push_back
#define x first
#define y second
int read()
{
	int x=0,f=1;char c;
	while((c=getchar())<'0' || c>'9') {if(c=='-') f=-1;}
	while(c>='0' && c<='9') {x=(x<<3)+(x<<1)+(c^48);c=getchar();}
	return x*f;
}
int n,k,ans,ch[M][2],c[M][2];vector<pii> v[M];
void dfs(int u)
{
	v[u].clear();
	if(!ch[u][0]) {v[u].pb({0,0});return ;}
	dfs(ch[u][0]);dfs(ch[u][1]);
	vector<pii> vc;
	for(int d=0;d<2;d++)
	{
		int ls=ch[u][d],rs=ch[u][d^1];
		int lc=c[u][d],rc=c[u][d^1],tmp=k-lc-rc;
		for(int i=0,j=0;i<v[ls].size();i++)
		{
			while(j+1<v[rs].size() && v[rs][j+1].x+v[ls][i].y<=tmp)
				j++;
			if(j>=v[rs].size() || v[rs][j].x+v[ls][i].y>tmp) continue;
			vc.pb({v[ls][i].x+lc,v[rs][j].y+rc});
		}
	}
	sort(vc.begin(),vc.end());
	for(auto t:vc)
	{
		if(!v[u].empty() && v[u].back().y<=t.y) continue;
		v[u].pb(t);
	}
}
signed main()
{
	n=read();
	for(int i=2;i<=n;i++)
	{
		int j=read(),w=ch[j][0]>0;
		ch[j][w]=i;c[j][w]=read();
	}
	int l=0,r=1e12;
	while(l<=r)
	{
		k=(l+r)>>1;dfs(1);
		if(v[1].empty()) l=k+1;
		else r=k-1,ans=k;
	}
	printf("%lld\n",ans);
}