#include <bits/stdc++.h>
using namespace std;
// #include<atcoder/all>
// using mint = atcoder::modint998244353;
using ld = long double;
#define fi first
#define se second
#define all(x) x.begin(),x.end()
#define rep(i,n) for(int i=0;i<(int)(n);++i)
template<typename T>bool chmin(T&a,T b){return b<a?(a=b,1):0;}
template<typename T>bool chmax(T&a,T b){return b>a?(a=b,1):0;}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int N,X;
    cin>>N>>X;
    vector<vector<int>> G(N);
    rep(i,N-1){
        int p;
        cin>>p;
        p--;
        G[p].push_back(i+1);
    }
    vector<long> C(N,0),S(N,0);
    rep(i,N-1)cin>>C[i+1]>>S[i+1];

    auto dfs=[&](auto dfs, int v)->vector<long> {
        vector<long> dp(S[v]+1, 1e18);
        dp[S[v]]=C[v];
        for(int e: G[v]){
            vector<long> ret=dfs(dfs, e);
            ret[0]=0;
            vector<long> np(ssize(dp)+ssize(ret),1e18);
            rep(i,ssize(ret)){
                rep(j,ssize(dp)){
                    chmin(np[i+j], ret[i]+dp[j]);
                }
            }
            swap(dp,np);
        }
        return dp;
    };
    vector<long> ret=dfs(dfs, 0);
    long ans=1e18;
    for(int i=X;i<ssize(ret);i++) chmin(ans, ret[i]);
    cout<<ans<<"\n";
}