#include<bits/stdc++.h>
#if __has_include(<atcoder/all>)
#endif
using namespace std;
#define eb emplace_back
#define LL(...) ll __VA_ARGS__;lin(__VA_ARGS__)
#define RDVL(T,n,...) vec<T>__VA_ARGS__;fe(refs(__VA_ARGS__),e)e.get().resizes(n);lin(__VA_ARGS__)
#define RDVV(T,n,...) vec<T>__VA_ARGS__;fe(refs(__VA_ARGS__),e)e.get().resizes(n);vin(__VA_ARGS__)
#define VL(n,...) RDVL(ll,n,__VA_ARGS__)
#define VV(n,...) RDVV(ll,n,__VA_ARGS__)
#define fo(i,...) for(auto[i,i##stop,i##step]=for_range<ll>(0,__VA_ARGS__);i<i##stop;i+=i##step)
#define fe(a,e,...) for(auto&&__VA_OPT__([)e __VA_OPT__(,__VA_ARGS__]):a)
#define ef(a,e,...) for(auto&&__VA_OPT__([)e __VA_OPT__(,__VA_ARGS__]):ranges::reverse_view(a))
#define defpp template<ostream&o=cout>void pp(const auto&...a){[[maybe_unused]]const char*c="";((o<<c<<a,c=" "),...);o<<'\n';}void epp(const auto&...a){pp<cerr>(a...);}
#define entry defpp void main();void main2();}int main(){my::io();my::main();}namespace my{
namespace my{
void io(){cin.tie(nullptr)->sync_with_stdio(0);cout<<fixed<<setprecision(15);}
using ll=long long;
constexpr auto refs(auto&...a){return array{ref(a)...};}
template<class T>constexpr auto for_range(T s,T b){T a=0;if(s)swap(a,b);return array{a-s,b,1-s*2};}
void lin(auto&...a){(cin>>...>>a);}
void vin(auto&...a){fo(i,(a.size()&...))(cin>>...>>a[i]);}
constexpr ll size10(auto x){x|=1;ll r=0;while(x>0)x/=10,++r;return r;}
template<class T>constexpr ll maxsize10(){return size10(numeric_limits<T>::max());}
bool amin(auto&a,const auto&b){return b<a?a=b,1:0;}
template<class A,class B=A>struct pair{
  A a;B b;
  pair()=default;
  pair(A a,B b):a(a),b(b){}
  auto operator<=>(const pair&)const=default;
};
template<bool is_negative=false>struct infinity{
  template<integral T>static constexpr T ones(size_t n){return n?ones<T>(n-1)*10+1:0;}
  template<integral T>constexpr operator T()const{return ones<T>(maxsize10<T>())*(1-is_negative*2);}
};
constexpr infinity oo;
template<class...A>using pack_back_t=tuple_element_t<sizeof...(A)-1,tuple<A...>>;
}
namespace my{
template<class V>concept vectorial=is_base_of_v<vector<typename remove_cvref_t<V>::value_type>,remove_cvref_t<V>>;
template<class V>istream&operator>>(istream&i,vector<V>&v){fe(v,e)i>>e;return i;}
template<class V>constexpr int depth=0;
template<vectorial V>constexpr int depth<V> =depth<typename V::value_type>+1;
template<class T>struct core_t_helper{using type=T;};
template<vectorial V>struct core_t_helper<V>{using type=typename core_t_helper<typename V::value_type>::type;};
template<class T>using core_t=core_t_helper<T>::type;
template<class V>struct vec;
template<int D,class T>struct hvec_helper{using type=vec<typename hvec_helper<D-1,T>::type>;};
template<class T>struct hvec_helper<0,T>{using type=T;};
template<int D,class T>using hvec=hvec_helper<D,T>::type;
template<class V>struct vec:vector<V>{
  static constexpr int D=depth<V>+1;
  using C=core_t<V>;
  using vector<V>::vector;
  vec(const auto&...a)requires(sizeof...(a)>=3){resizes(a...);}
  void resizes(const auto&...a){if constexpr(sizeof...(a)==D)*this=make(a...,C{});else*this=make(a...);}
  static auto make(ll n,const auto&...a){
    if constexpr(sizeof...(a)==1)return vec<C>(n,array{a...}[0]);
    else return vec<decltype(make(a...))>(n,make(a...));
  }
  vec&operator--(){fe(*this,e)--e;return*this;}
  ll size()const{return vector<V>::size();}
  auto&emplace_front(auto&&...a){this->emplace(this->begin(),std::forward<decltype(a)>(a)...);return*this;}
  auto&emplace_back(auto&&...a){vector<V>::emplace_back(std::forward<decltype(a)>(a)...);return*this;}
  vec slice(ll l,ll r)const{return l<r?vec(this->begin()+l,this->begin()+r):vec{};}
  template<class T=C>auto fold(auto&&f)const{
    pair<T,bool>res{};
    fe(*this,e){
      if constexpr(!vectorial<V>){
        if(res.b)f(res.a,e);
        else res={e,1};
      }else { }

    }
    return res;
  }
  template<class T=C>auto sum()const{return fold<T>([](auto&a,const auto&b){a+=b;}).a;}
  auto min()const{return fold([](auto&a,auto b){if(b<a)a=b;}).a;}
};
template<class...A>requires(sizeof...(A)>=2)vec(const A&...a)->vec<hvec<sizeof...(A)-2,pack_back_t<A...>>>;
}
namespace my{
template<class T>struct queue:std::queue<T>{
  queue()=default;
  queue(const initializer_list<T>&a){fe(a,e)this->emplace(e);}
  ll size()const{return std::queue<T>::size();}
  T pop(){T r=this->front();std::queue<T>::pop();return r;}
};
}
namespace my{
template<class WT>struct edge{
  int from,to;
  WT wt;
  int id;
  edge()=default;
  edge(int from,int to,WT wt=1,int id=-1):from(from),to(to),wt(wt),id(id){}
};
}
namespace my{
template<class WT>class RootedTree{
public:
  ll n_;
  vec<vec<edge<WT>>>edges_;
  vec<edge<WT>>rev_edge_;
  int root_;
  RootedTree()=default;
  RootedTree(ll n,ll r):n_(n),edges_(n),rev_edge_(n,{-1,-1,WT{},-1}),root_(r){}
  decltype(auto)operator[](ll i){return edges_[i];}
  void set_edge(const edge<WT>&e){
    edges_[e.from].eb(e);
    rev_edge_[e.to]=e;
  }
  auto bfs_order(ll start=-1)const{
    if(start==-1)start=root_;
    vec<ll>ord;
    queue<ll>q{start};
    while(q.size()){
      ll u=q.pop();
      ord.eb(u);
      fe(edges_[u],e)q.emplace(e.to);
    }
    return ord;
  }
};
}
namespace my{
template<class WT>class Graph{
public:
  ll n_;
  vec<vec<edge<WT>>>edges_;
  Graph()=default;
  Graph(ll n):n_(n),edges_(n){}
  auto&add_edges(const vec<ll>&p){fo(i,p.size())if(p[i]!=-1)edges_[p[i]].eb(p[i],i,1,i);return*this;}
  vec<int>buf;
  int count=0;
  auto bfs_tree(int s)const{
    RootedTree<WT>tree(n_,s);

    vec<bool>used(n_);
    queue<edge<WT>>q{{-1,s,WT{},-1}};
    while(q.size()){
      auto pu=q.pop();
      auto u=pu.to;
      if(used[u])continue;
      used[u]=1;

      if(pu.from!=-1)tree.set_edge(pu);

      fe(edges_[u],e)if(!used[e.to])q.emplace(e);
    }
    return tree;
  }
};
}
namespace my{entry
void main(){
  LL(N,X);
  VL(N-1,p);--p;
  p.emplace_front(-1);
  Graph<ll>tmp(N);
  auto g=tmp.add_edges(p).bfs_tree(0);

  VV(N-1,c,s);
  c.emplace_front(0);
  s.emplace_front(0);

  vec dp(N,1,ll(oo));
  ef(g.bfs_order(),u){
    dp[u][0]=0;
    fe(g[u],e){
      ll v=e.to;
      ll n=dp[u].size();
      ll m=dp[v].size();
      vec nx(n+m-1,ll(oo));
      fo(j,n)fo(k,m)amin(nx[j+k],dp[u][j]+dp[v][k]);
      swap(dp[u],nx);
    }

    vec tmp(dp[u].size()+s[u],ll(oo));
    tmp[0]=0;
    fo(j,dp[u].size())tmp[j+s[u]]=dp[u][j]+c[u];
    swap(dp[u],tmp);
  }

  pp(dp[0].slice(X,s.sum()+1).min());
}}