#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, x;
  cin >> n >> x;
  VVI to(n);
  for (int i = 1; i < n; i++) {
    int p;
    cin >> p;
    to[p-1].emplace_back(i);
  }
  VI c(n), s(n);
  for (int i = 1; i < n; i++) cin >> c[i] >> s[i];
  constexpr long long INF = 1002003004005006007;
  auto dfs = [&](auto&& self, int u) -> VL {
    VL res{0};
    for (int v : to[u]) {
      auto r = self(self, v);
      static VL tmp;
      int sz1 = res.size(), sz2 = r.size();
      tmp.assign(sz1 + sz2 - 1, INF);
      rep(i, sz1) rep(j, sz2) chmin(tmp[i+j], res[i] + r[j]);
      res = tmp;
    }
    for (auto& x : res) x += c[u];
    res.insert(res.begin(), s[u], INF);
    res[0] = 0;
    return res;
  };
  auto res = dfs(dfs, 0);
  ll ans = INF;
  for (ll x : res | views::drop(x)) chmin(ans, x);
  cout << ans << '\n';
}