#include<bits/stdc++.h>
using namespace std;

int main(){
  using ll=long long;
  ll inf=1e18;
  int n,x;
  cin>>n>>x;
  vector<vector<int>> g(n);
  vector<ll> c(n),s(n);
  for (int i=1;i<n;i++){
    int p;
    cin>>p;
    p--;
    g[p].push_back(i);
  }
  int m=0;
  for (int i=1;i<n;i++){
    cin>>c[i]>>s[i];
    m+=s[i];
  }
  vector<int> sum(n);
  vector<vector<ll>> dp(n,vector<ll>(m+1,inf));
  auto dfs=[&](auto dfs,int v,int par)-> void {
    dp[v][s[v]]=c[v];
    sum[v]+=s[v];
    for (int u:g[v]){
      dfs(dfs,u,v);
      auto next=dp[v];
      for (int i=0;i<=m;i++){
        for (int j=0;j<=m;j++){
          if (i+j>m) break;
          next[i+j]=min(next[i+j],dp[v][i]+dp[u][j]);
        }
      }
      swap(next,dp[v]);
      sum[v]+=sum[u];
    }
    dp[v][0]=0;
  };
  dfs(dfs,0,-1);
  cout<<dp[0][x]<<endl;
}