#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
    int N,X;
    cin>>N>>X;
    vector<vector<int>> G(N);
    for(int i=1;i<N;i++){
        int a;
        cin>>a;
        a--;
        G[a].push_back(i);
    }
    vector<int> c(N), s(N);
    for(int i=1;i<N;i++) cin>>c[i]>>s[i];
    vector<int> C(N,1);
    auto cs = [&](auto &&self, int a) -> void {
        for(int x:G[a]){
            self(self,x);
            C[a] += C[x];
        }
    };
    cs(cs,0);
    int inf = 1e16;
    vector<vector<int>> dp(N+1,vector<int>(X+1,inf));
    int id = 0;
    dp[0][0] = 0;
    auto fs = [&](auto &&self, int a) -> void {
        for(int i=0;i<=X;i++){
            dp[id+C[a]][i] = min(dp[id+C[a]][i],dp[id][i]);
            dp[id+1][min(X,i+s[a])] = min(dp[id+1][min(X,i+s[a])],dp[id][i]+c[a]);
        }
        id++;
        for(int x:G[a]){
            self(self,x);
            C[a] += C[x];
        }
    };
    fs(fs,0);
    int ans = inf;
    for(int i=0;i<=N;i++) ans = min(ans,dp[i][X]);
    cout<<ans<<endl;
}