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

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
 
    int N,X; cin >> N >> X;
    vector<vector<int>> Graph(N);
    for(int i=0; i<N-1; i++){
        int u,v = i+1; cin >> u; u--;
        Graph.at(u).push_back(v);
    }
    vector<pair<long long,int>> CS(N-1);
    for(auto &[c,s] : CS) cin >> c >> s;
    CS.insert(CS.begin(),{0,0});
    long long inf = 1e18;
    auto dfs = [&](auto dfs,int pos) -> vector<long long> {
        vector<long long> ret = {0};
        for(auto to : Graph.at(pos)){
            auto kid = dfs(dfs,to);
            if(kid.size() > ret.size()) swap(ret,kid);
            int n = kid.size();
            ret.resize(ret.size()+n,inf);
            int m = ret.size();
            for(int k=m-1-1; k>=0; k--) if(ret.at(k) < inf){
                for(int i=1; i<n; i++) if(kid.at(i) < inf){
                    if(i+k >= m) break;
                    ret.at(k+i) = min(ret.at(k+i),ret.at(k)+kid.at(i));
                }
            }
            while(ret.back() == inf) ret.pop_back();
        }
        reverse(ret.begin(),ret.end());
        auto [c,s] = CS.at(pos);
        for(auto &v : ret) v += c;
        while(s--) ret.push_back(inf);
        reverse(ret.begin(),ret.end());
        ret.at(0) = 0;
        return ret;
    };
    auto dp = dfs(dfs,0);
    long long answer = inf; 
    for(int i=X; i<dp.size(); i++) answer = min(answer,dp.at(i));
    cout << answer << endl;
}