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

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int N, X;
    cin >> N >> X;
    vector<int> p(N);
    for(int v = 1; v < N; v++) cin >> p[v], p[v]--;
    vector<pair<int,int>> a(N);
    for(int v = 1; v < N; v++){
        auto &&[c, s] = a[v];
        cin >> c >> s;
    }
    vector dp(N, vector<ll>(1));
    for(int v = N - 1; v >= 1; v--){
        auto [c, s] = a[v];
        int sz = dp[p[v]].size(), m = sz + dp[v].size() + s - 1;
        auto ndp = dp[p[v]];
        ndp.resize(m, 1ll << 60);
        for(int i = 0; i < sz; i++){
            for(int j = 0; j < dp[v].size(); j++){
                ndp[i + j + s] = min(ndp[i + j + s], dp[p[v]][i] + dp[v][j] + c);
            }
        }
        swap(ndp, dp[p[v]]);
    }
    ll ans = 1ll << 60;
    for(int i = X; i < dp[0].size(); i++) ans = min(ans, dp[0][i]);
    cout << ans << '\n';
}