#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define vi vector<int>
#define vl vector<ll>
#define vii vector<pair<int,int>>
#define vll vector<pair<ll,ll>>
#define vvi vector<vector<int>>
#define vvl vector<vector<ll>>
#define vvii vector<vector<pair<int,int>>>
#define vvll vector<vector<pair<ll,ll>>>
#define vst vector<string>
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define mkunique(x) sort(all(x));(x).erase(unique(all(x)),(x).end())
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=2005;
const ll INF=15LL<<58;

ll dp[MAX][MAX];
ll sz[MAX];
ll c[MAX],s[MAX];

vi G[MAX];

void solve(int u){
    sz[u]=s[u];
    vector<ll> co(sz[u]+1,INF);
    co[s[u]]=c[u];
    for(int to:G[u]){
        solve(to);
        vector<ll> ne(sz[u]+sz[to]+1,INF);
        for(int i=0;i<=sz[u];i++){
            for(int j=0;j<=sz[to];j++){
                chmin(ne[i+j],co[i]+dp[to][j]);
            }
        }
        co=ne;
        sz[u]+=sz[to];
    }
    for(int i=0;i<=sz[u];i++){
        dp[u][i]=co[i];
    }
    dp[u][0]=0;
}

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int N;cin>>N;
    for(int i=0;i<MAX;i++) for(int j=0;j<MAX;j++) dp[i][j]=INF;
    ll X;cin>>X;
    for(int i=1;i<N;i++){
        int p;cin>>p;p--;
        G[p].pb(i);
    }
    
    for(int i=1;i<N;i++){
        cin>>c[i]>>s[i];
    }
    
    solve(0);
    ll ans=INF;
    for(int i=X;i<=2000;i++) chmin(ans,dp[0][i]);
    cout<<ans<<endl;
}