#include<bits/stdc++.h>
#define sqr(x) ((x)*(x))
#define ll long long
#define ull unsigned long long
#define ui unsigned int
#define ld long double
#define vi vector<int>
#define HEAP(...) priority_queue<__VA_ARGS__ >
#define heap(...) priority_queue<__VA_ARGS__,vector<__VA_ARGS__ >,greater<__VA_ARGS__ > > 
#define pii pair<ll,ll> 
#define pb push_back
#define mp make_pair
#define debuge cerr<<"isok"<<endl
#define debug(x) cerr<<#x<<"="<<x<<endl
#define dprintf(...) fprintf(stderr,__VA_ARGS__)
#define SS second
#define FF first
#define ls (k<<1)
#define rs (k<<1|1)
#define clr(a,x) memset(a,x,sizeof(a))
#define cpy(a,x) memcpy(a,x,sizeof(a))
#define file(x) freopen(x".in","r",stdin),freopen(x".out","w",stdout)
#define SZ(x) ((int)x.size())
using namespace std;
template<class T> inline void gmin(T &x,const T &y){if(x>y) x=y;}
template<class T> inline void gmax(T &x,const T &y){if(x<y) x=y;}
const int BufferSize=1<<16;
char buffer[BufferSize],*Bufferhead,*Buffertail;
bool Terminal;
inline char Getchar(){
	if(Bufferhead==Buffertail){
		int l=fread(buffer,1,BufferSize,stdin);
		if(!l){Terminal=1;return 0;}
		Buffertail=(Bufferhead=buffer)+l;
	}
	return *Bufferhead++;
}
template<class T>inline bool read(T &x){
	x=0;char c=Getchar(),rev=0;
	while(c<'0'||c>'9'){rev|=c=='-';c=Getchar();if(Terminal)return 0;}
	while(c>='0'&&c<='9') x=x*10+c-'0',c=Getchar();
	if(c=='.'){
		c=Getchar();double t=0.1;
		while(c>='0'&&c<='9') x=x+(c-'0')*t,c=Getchar(),t=t/10;
	}
	x=rev?-x:x;
	return 1;
}
template<class T1,class T2> inline bool read(T1 &x,T2 &y){return read(x)&read(y);}
template<class T1,class T2,class T3> inline bool read(T1 &x,T2 &y,T3 &z){return read(x)&read(y)&read(z);}
template<class T1,class T2,class T3,class T4> inline bool read(T1 &x,T2 &y,T3 &z,T4 &w){return read(x)&read(y)&read(z)&read(w);}
inline bool reads(char *x){
	char c=Getchar();
	while(c<33||c>126){c=Getchar();if(Terminal)return 0;}
	while(c>=33&&c<=126) (*x++)=c,c=Getchar();
	*x=0;return 1;
}
template<class T>inline void print(T x,const char c='\n'){
	if(!x){putchar('0');putchar(c);return;}
	if(x<0) putchar('-'),x=-x;
	int m=0,a[20];
	while(x) a[m++]=x%10,x/=10;
	while(m--) putchar(a[m]+'0');
	putchar(c);
}
//--------------------------------head---------------------------------------------

const ll inf=1ll<<50;
const int N=131105,M=N*18,mod=1e9+7;
template<class T,class S> inline void ch(T &x,const S y){x=(x+y)%mod;}
inline int exp(int x,int y,const int mod=::mod){
	int ans=1;
	while(y){
		if(y&1) ans=(ll)ans*x%mod;
		x=(ll)x*x%mod;y>>=1;
	}return ans;
}

int n,tot,st[N],len[N];
ll d;
vector<pii> g[N];
pii tmp[N],t1[N],t2[N],a[M];
bool val[N];

void Sort(int c1,int c2){
	int cnt=1,x=1,y=1;
	while(x<=c1&&y<=c2)
		if(t1[x]<t2[y]) tmp[cnt++]=t1[x++]; else tmp[cnt++]=t2[y++];
	while(x<=c1) tmp[cnt++]=t1[x++];
	while(y<=c2) tmp[cnt++]=t2[y++];
}

inline void dfs(int x,int w=0){
	val[x]=1;
	if(!g[x].size()){
		st[x]=tot;len[x]=1;tot++;
		a[tot]=mp((ll)w,(ll)w);
		return;
	}
	int L=g[x][0].FF,lw=g[x][0].SS;
	int R=g[x][1].FF,rw=g[x][1].SS;
	dfs(L,lw);dfs(R,rw);
	val[x]=val[L]&val[R];
	if(!val[x]) return;
	int c1=0,c2=0,cnt=0;
	for(int i=1,l=1,r=len[R];i<=len[L];i++){
		ll x=a[st[L]+i].FF;
		while(l<=len[R]&&a[st[R]+l].SS+x>d) l++;
		while(r&&a[st[R]+r].FF+x>d) r--;
		ll t=inf;
		if(l<=len[R]) gmin(t,a[st[R]+l].FF);
		if(r) gmin(t,a[st[R]+r].SS);
		if(t<inf) t1[++c1]=mp(a[st[L]+i].SS,t);
	}
	for(int i=len[L],l=1,r=len[R];i;i--){
		ll x=a[st[L]+i].SS;
		while(l<=len[R]&&a[st[R]+l].SS+x>d) l++;
		while(r&&a[st[R]+r].FF+x>d) r--;
		ll t=inf;
		if(l<=len[R]) gmin(t,a[st[R]+l].FF);
		if(r) gmin(t,a[st[R]+r].SS);
		if(t<inf) t2[++c2]=mp(a[st[L]+i].FF,t);
	}
	cnt=c1+c2;
	if(!cnt){val[x]=0;return;}
	if(x==1) return;
	Sort(c1,c2);
	st[x]=tot;
	sort(tmp+1,tmp+cnt+1);
	len[x]=1;a[st[x]+1]=tmp[1];
	for(int i=2;i<=cnt;i++)
		if(tmp[i].SS<a[st[x]+len[x]].SS) len[x]++,a[st[x]+len[x]]=tmp[i];
	for(int i=1;i<=len[x];i++)
		a[st[x]+i].FF+=w,a[st[x]+i].SS+=w;
	tot+=len[x];
}
inline bool check(ll mid){
	d=mid;tot=0;
	dfs(1);
	return val[1];
}

int main(){
#ifdef rqgao2014
	freopen("input.txt","r",stdin);
#endif
	scanf("%d",&n);
	for(int i=2;i<=n;i++){
		int x,v;scanf("%d%d",&x,&v);
		g[x].pb(mp(i,v));
	}
	ll l=0,r=1ll<<35;
	while(l<r){
		ll mid=l+r>>1;
		if(check(mid)) r=mid; else l=mid+1;
	}
	printf("%lld\n",r);
	return 0;
}

Measured memory_bytes: 24064