#include<bits/stdc++.h>
#include<atcoder/all>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
using namespace atcoder;
typedef long long ll;
typedef pair<int, int> P;

template <int m> ostream& operator<<(ostream& os, const static_modint<m>& a) {os << a.val(); return os;}
template <int m> ostream& operator<<(ostream& os, const dynamic_modint<m>& a) {os << a.val(); return os;}
template <int m> istream& operator>>(istream& is, static_modint<m>& a) {long long x; is >> x; a = x; return is;}
template <int m> istream& operator>>(istream& is, dynamic_modint<m>& a) {long long x; is >> x; a = x; return is;}
template<typename T> istream& operator>>(istream& is, vector<T>& v){int n = v.size(); assert(n > 0); rep(i, n) is >> v[i]; return is;}
template<typename U, typename T> ostream& operator<<(ostream& os, const pair<U, T>& p){os << p.first << ' ' << p.second; return os;}
template<typename T> ostream& operator<<(ostream& os, const vector<T>& v){int n = v.size(); rep(i, n) os << v[i] << (i == n - 1 ? "\n" : " "); return os;}
template<typename T> ostream& operator<<(ostream& os, const vector<vector<T>>& v){int n = v.size(); rep(i, n) os << v[i] << (i == n - 1 ? "\n" : ""); return os;}
template<typename T> ostream& operator<<(ostream& os, const set<T>& se){for(T x : se) os << x << " "; os << "\n"; return os;}
template<typename T> ostream& operator<<(ostream& os, const unordered_set<T>& se){for(T x : se) os << x << " "; os << "\n"; return os;}
template<typename S, auto op, auto e> ostream& operator<<(ostream& os, const atcoder::segtree<S, op, e>& seg){int n = seg.max_right(0, [](S){return true;}); rep(i, n) os << seg.get(i) << (i == n - 1 ? "\n" : " "); return os;}
template<typename S, auto op, auto e, typename F, auto mapping, auto composition, auto id> ostream& operator<<(ostream& os, const atcoder::lazy_segtree<S, op, e, F, mapping, composition, id>& seg){int n = seg.max_right(0, [](S){return true;}); rep(i, n) os << seg.get(i) << (i == n - 1 ? "\n" : " "); return os;}

template<typename T> void chmin(T& a, T b){a = min(a, b);}
template<typename T> void chmax(T& a, T b){a = max(a, b);}

const long long INF = 1001001001001001;

int main(){
	int n, x;
	cin >> n >> x;
	vector<vector<int>> children(n);
	for(int i = 1; i < n; i++){
		int p;
		cin >> p;
		p--;
		children[p].push_back(i);
	}
	vector<long long> c(n);
	vector<int> s(n);
	for(int i = 1; i < n; i++) cin >> c[i] >> s[i];
	auto solve = [&](int from, auto solve) -> vector<long long>{
		vector<long long> dp = {0LL};
		for(auto to : children[from]){
			auto ep = solve(to, solve);
			vector<long long> dp_new(dp.size() + ep.size() - 1, INF);
			for(int i = 0; i < int(dp.size()); i++){
				for(int j = 0; j < int(ep.size()); j++){
					chmin(dp_new[i + j], dp[i] + ep[j]);
				}
			}
			swap(dp, dp_new);
		}
		{
			vector<long long> dp_new(dp.size() + s[from], INF);
			for(int i = 0; i < int(dp.size()); i++){
				chmin(dp_new[i + s[from]], dp[i] + c[from]);
			}
			dp_new[0] = 0;
			swap(dp, dp_new);
		}
		return dp;
	};
	auto dp = solve(0, solve);
	long long ans = INF;
	for(int i = x; i < int(dp.size()); i++){
		chmin(ans, (long long)dp[i]);
	}
	cout << ans << "\n";
	cerr << dp;
	
	return 0;
}