#include<bits/stdc++.h>
#ifndef LOCAL
#define cerr if(false)cerr
#endif // LOCAL
using namespace std;
using ll = long long;
const int N = 1e6 + 66;
ll ans;
vector<pair<int,int>>g[N];
priority_queue<ll>ql;
priority_queue<ll, vector<ll>, greater<ll>>qr;
pair<ll,ll> dfs(int v) {
if (g[v].empty()) return {0, 0};
vector<pair<ll,ll>>now;
for (auto [to, c] : g[v]) {
auto [nl, nr] = dfs(to);
now.emplace_back(nl + c, nr + c);
}
while(ql.size())ql.pop();
while(qr.size())qr.pop();
for (auto [l, r] : now) {
if (ql.empty() || qr.empty()) {
assert(ql.empty() && qr.empty());
ql.push(l);
qr.push(r);
continue;
}
ll L = ql.top(), R = qr.top();
if (r <= L) {
ql.push(l);
ql.push(r);
ans += ql.top() - r;
qr.push(ql.top());
ql.pop();
} else if (l >= R) {
qr.push(l);
qr.push(r);
ans += l - qr.top();
ql.push(qr.top());
qr.pop();
} else {
ql.push(l);
qr.push(r);
}
}
ll L = ql.top(), R = qr.top();
return {L, R};
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0), cout.tie(0);
int n, m;
cin >> n >> m;
for (int i = 2 ; i <= n + m ; ++ i) {
int p, c;
cin >> p >> c;
g[p].emplace_back(i, c);
}
dfs(1);
cout << ans;
}
