#include <bits/stdc++.h>
typedef long long ll;
const ll inf = 1e15;
int main() {
// std::ios_base::sync_with_stdio(false);
// std::cin.tie(nullptr);
ll n, m;
std::cin >> n >> m;
std::vector<std::vector<std::pair<ll, ll>>> adj(n + m + 1);
std::vector<ll> arr;
for (ll i = 2, p, c; i <= n + m; ++ i) {
std::cin >> p >> c;
arr.push_back(c);
adj[i].push_back({p, c});
adj[p].push_back({i, c});
}
if (n == 1) {
std::sort(arr.begin(), arr.end());
ll ans = 0;
for (auto &i : arr) {
ans += std::abs(arr[arr.size() / 2] - i);
}
std::cout << ans << "\n";
return 0;
}
if (n + m <= 300) {
std::vector<ll> nodes;
std::vector<ll> pars(n + m + 1);
std::function<void(ll, ll)> topological_sort;
topological_sort = [&](ll node, ll par) {
pars[node] = par;
for (auto &i : adj[node]) {
if (i.first == par) continue;
topological_sort(i.first, node);
}
nodes.push_back(node);
};
topological_sort(1, 0);
std::vector<std::vector<ll>> dp(n + m + 1, std::vector<ll>(301));
for (ll val = 0; val <= 300; ++ val) {
for (auto &node : nodes) {
ll node_cnt = 0;
for (auto &child : adj[node]) {
if (child.first == pars[node]) continue;
node_cnt++;
ll cur = inf;
for (ll i = 0; i <= val; ++ i) {
cur = std::min(cur, std::abs(child.second - i) + dp[child.first][val - i]);
}
dp[node][val] += cur;
}
if (node_cnt == 0) dp[node][val] = inf * (val != 0);
else if (dp[node][val] > inf) dp[node][val] = inf;
}
}
ll ans = inf;
for (ll val = 0; val <= 300; ++ val) {
ans = std::min(ans, dp[1][val]);
}
std::cout << ans << "\n";
return 0;
}
}
