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

using isize = size_t;
using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
using i128 = __int128_t;
using u128 = __uint128_t;
using f64 = long double;
using p2 = pair<i64, i64>;
using el = tuple<i64, i64, i64>;
using mint = atcoder::modint998244353;

void _main();
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(18);
  _main();
}

i64 pow(i64 x, i64 n) {
  i64 res = 1;
  i64 t = x;
  while (n > 0) {
    if (n & 1) res *= t;
    t *= t;
    n >>= 1;
  }
  return res;
}
i64 pow(i64 x, i64 n, i64 m) {
  i64 res = 1;
  i64 t = x % m;
  while (n > 0) {
    if (n & 1) res = res * t % m;
    t = t * t % m;
    n >>= 1;
  }
  return res;
}

i64 n, x;
vector<i64> dp[2000];
vector<i64> g[2000];
i64 s[2000], c[2000];
void dfs(i64 v) {
  dp[v] = vector<i64>(s[v] + 1, 1e18);
  dp[v][s[v]] = c[v];
  for (i64 nv : g[v]) {
    dfs(nv);
    vector<i64> ndp(dp[v].size() + dp[nv].size() - 1, 1e18);
    for (i64 i = 0; i < dp[v].size(); i++) {
      ndp[i] = min(ndp[i], dp[v][i]);
      for (i64 j = 0; j < dp[nv].size(); j++) {
        ndp[i + j] = min(ndp[i + j], dp[v][i] + dp[nv][j]);
      }
    }
    swap(ndp, dp[v]);
  }
}
void _main() {
  cin >> n >> x;
  for (i64 i = 1; i < n; i++) {
    i64 p;
    cin >> p;
    p--;
    g[p].push_back(i);
  }
  s[0] = c[0] = 0;
  for (i64 i = 1; i < n; i++) {
    cin >> c[i] >> s[i];
  }
  dfs(0);
  i64 ans = 1e18;
  for (i64 i = x; i < dp[0].size(); i++) ans = min(ans, dp[0][i]);
  cout << ans << "\n";
}