#include<vector>

#include<cstdio>

#include<cstring>

#include<algorithm>

using namespace std;

typedef long long ll;

const int N = ;

template<typename T>

inline void read(T&x)

{

    T f = ,c = ;char ch=getchar();

    while(ch<''||ch>''){if(ch=='-')f=-;ch=getchar();}

    while(ch>=''&&ch<=''){c=c*+ch-'';ch=getchar();}

    x = f*c;

}

int n,fa[N],ch[N][];

ll v[N],dep[N];

void DFS(int u)

{

    if(!ch[u][])return ;

    dep[ch[u][]]=dep[u]+v[ch[u][]],DFS(ch[u][]);

    dep[ch[u][]]=dep[u]+v[ch[u][]],DFS(ch[u][]);

}

struct Pair

{

    ll x,y;

    Pair(){}

    Pair(ll x,ll y):x(x),y(y){}

}g1[N],g2[N],g[N];

vector<Pair>ve[N];

ll mid;

int Merge(int len)

{

    int i = ,j = len,k = ;

    while(i<=len&&j>=)

    {

        if(g1[i].x<=g2[j].x)g[++k]=g1[i++];

        else g[++k]=g2[j--];

    }

    while(i<=len)g[++k]=g1[i++];

    while(j>=)g[++k]=g2[j--];

    return k;

}

void dfs(int u)

{

    if(!ch[u][]){ve[u].push_back(Pair(dep[u],dep[u]));return ;}

    int ls = ch[u][],rs = ch[u][];

    dfs(ls),dfs(rs);int k=;

    if(ve[ls].size()>ve[rs].size())swap(ls,rs);

    for(int i=,j=-,l1=ve[ls].size(),l2=ve[rs].size();i<l1;i++)

    {

        while(j<l2-&&ve[ls][i].y+ve[rs][j+].x-2ll*dep[u]<=mid)j++;

        if(~j)g1[++k]=Pair(ve[ls][i].x,ve[rs][j].y),g2[k]=Pair(ve[rs][j].y,ve[ls][i].x);

    }

    int len = Merge(k);

    for(int i=;i<=len;i++)

        if(i==||g[i].y<g[i-].y)

            ve[u].push_back(g[i]);

}

bool check()

{

    for(int i=;i<=n;i++)

        ve[i].clear();

    dfs();

    return (int)ve[].size()>;

}

int main()

{

    read(n);

    for(int i=;i<=n;i++)

    {

        read(fa[i]),read(v[i]);

        if(!ch[fa[i]][])ch[fa[i]][]=i;

        else ch[fa[i]][]=i;

    }

    DFS();

    ll l = ,r = 200000ll*n,ans = r;

    while(l<=r)

    {

        mid = (l+r)>>;

        if(check())ans=mid,r=mid-;

        else l=mid+;

    }

    printf("%lld\n",ans);

    return ;

}