#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
#include <stdlib.h>
#include <atcoder/all>
using namespace atcoder;
using namespace std;
#define rep(i, a, n) for(ll i = a; i < n; i++)
#define rrep(i, a, n) for(ll i = a; i >= n; i--)
#define inr(l, x, r) (l <= x && x < r)
#define ll long long
#define ld long double
#define pii pair<int, int>
#define pll pair<ll, ll>
#define all(x) (x).begin(), (x).end()
//constexpr ll MOD = 1000000007;
constexpr ll MOD = 998244353;
constexpr int IINF = 1001001001;
constexpr ll INF = 1LL<<60;
template<class t,class u> void chmax(t&a,u b){if(a<b)a=b;}
template<class t,class u> void chmin(t&a,u b){if(b<a)a=b;}

using mint = modint998244353;

ll gcd(ll a, ll b){
    if(a%b == 0){
      return b;
    }else{
      return gcd(b, a%b);
    }
}

ll lcm(ll a, ll b){
    return a*b / gcd(a, b);
}

ll powMod(ll x, ll n, ll mod) {
    if (n == 0) return 1 % mod;
    ll val = powMod(x, n / 2, mod);
    val *= val;
    val %= mod;
    if (n % 2 == 1) val *= x;
    return val % mod;
}

int main() {
    ll n, x; cin >> n >> x;
    vector<ll> p(n), c(n,0), s(n,0);
    ll sum = 0, sum2 = 0;
    vector<vector<ll>> g(n);
    rep(i,1,n) cin >> p[i], p[i]--;
    rep(i,1,n) g[p[i]].push_back(i);
    rep(i,1,n) cin >> c[i] >> s[i], sum += s[i], sum2 += c[i];
    ll px = sum-x+1;
    vector<vector<ll>> dp(n);
    auto dfs = [&](auto& self, int v) -> pll {
        vector<ll> use = {0};
        pll ss = {c[v], s[v]};
        for(auto nv : g[v]){
            auto [nc, ns] = self(self, nv);
            ss.first += nc;
            ss.second += ns;
            vector<ll> nuse(min((ll)(use.size()+dp[nv].size()-1),px+1), -INF);
            rep(i,0,use.size()) rep(j,0,dp[nv].size()){
                if(i + j > px) break;
                chmax(nuse[i+j], use[i] + dp[nv][j]);
            }
            use = nuse;
        }
        chmin(ss.second,px);
        while(ss.second >= use.size()) use.push_back(-INF);
        use[ss.second] = max(use[ss.second], ss.first);
        dp[v] = use;
        return ss;
    };
    dfs(dfs,0);
    ll ans = INF;
    rep(i,0,dp[0].size()){
        if(i < px && dp[0][i] >= 0) chmin(ans, sum2 - dp[0][i]);
        // cout << px << " " << i << " " << dp[0][i] << " " << sum2 - dp[0][i] << endl;
    }
    // rep(i,0,n){
    //     for(auto xx: dp[i]) cout << xx << " ";
    //     cout << endl;
    // }
    cout << ans << endl;
    return 0;
}