#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 300300;
bool leaf[N];
vector<pair<int, ll>> adj[N];
ll ans[N];
priority_queue<ll> l[N];
priority_queue<ll, vector<ll>, greater<ll>> r[N];
void dfs(int v, ll p = 0ll, ll d = 0ll) {
if (leaf[v]) {
l[v].push(p);
r[v].push(p);
return;
}
for (auto& [x, w] : adj[v]) {
dfs(x, w, d + w);
ans[v] += ans[x];
if (l[v].empty()) {
swap(l[v], l[x]);
swap(r[v], r[x]);
continue;
}
if (l[x].size() + r[x].size() > l[v].size() + r[v].size()) {
swap(l[v], l[x]);
swap(r[v], r[x]);
}
while (!l[x].empty()) {
ll now = l[x].top();
l[x].pop();
ll nowr = r[v].top();
if (now <= nowr) l[v].push(now);
else {
ans[v] += now - nowr;
l[v].push(nowr);
r[v].pop();
r[v].push(now);
}
}
while (!r[x].empty()) {
ll now = r[x].top();
r[x].pop();
ll nowl = l[v].top();
if (nowl <= now) r[v].push(now);
else {
ans[v] += nowl - now;
r[v].push(nowl);
l[v].pop();
l[v].push(now);
}
}
}
ll nl = l[v].top() + p;
l[v].pop();
l[v].push(nl);
ll nr = r[v].top() + p;
while (!r[v].empty()) r[v].pop();
r[v].push(nr);
}
int main() {
cin.tie(nullptr)->sync_with_stdio(false);
int n, m;
cin >> n >> m;
for (int i = 2;i <= n + m;i++) {
int p;
ll c;
cin >> p >> c;
adj[p].push_back({ i, c });
}
for (int i = n + 1;i <= n + m;i++) leaf[i] = 1;
dfs(1);
cout << ans[1] << '\n';
return 0;
}
