#include <bits/stdc++.h>
using namespace std;
template<typename T>
struct Line {
T m, b;
Line() : m(T()), b(T()) {}
Line(T _m, T _b) : m(_m), b(_b) {}
// T operator()(long long x) { return m * x + b; }
// friend long double intersect(const Line &l1, const Line &l2) {
// return (long double)(l2.b - l1.b) / (long double)(l1.m - l2.m);
// }
// friend ostream& operator<<(ostream &os, const Line &l) {
// return os << '{' << l.m << "x + " << l.b << '}';
// }
};
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
int N, M;
cin >> N >> M;
M += N;
vector<long long> C(M);
vector<vector<int>> T(M);
for (int i = 1; i < M; i++) {
int p;
long long c;
cin >> p >> c;
T[p - 1].push_back(i);
C[i] = c;
}
vector<Line<long long>> L(M);
vector<priority_queue<long long>> Q(M);
const auto dfs = [&](const auto &self, int u) -> void {
priority_queue<long long> &pq = Q[u];
if (T[u].empty()) {
L[u].m = 1, L[u].b = -C[u];
pq.push(C[u]);
pq.push(C[u]);
return;
}
for (int v : T[u]) {
self(self, v);
L[u].m += L[v].m, L[u].b += L[v].b;
if (Q[v].size() > pq.size())
pq.swap(Q[v]);
while (!Q[v].empty()) {
pq.push(Q[v].top());
Q[v].pop();
}
}
while (L[u].m > 1) { // slope is never greater than 1
long long x = pq.top(); pq.pop();
L[u].m--, L[u].b += x; // compensate for change in slope
}
long long t0 = pq.top(); pq.pop(); // location of slope 0 -> 1
long long t1 = pq.top(); pq.pop(); // location of slope -1 -> 0
pq.push(t0 + C[u]); // slope = -1 section increases by C[u]
pq.push(t1 + C[u]); // slope = 0 section increases by C[u]
L[u].b -= C[u]; // L[u].m = 1, compensate for adding C[u] to previous sections
};
dfs(dfs, 0);
// since f(x) is CCU <-> f"(x) >= 0, max f(x) for all x is at f'(x) = 0
priority_queue<long long> &pq = Q[0];
while (L[0].m > 0) {
long long x = pq.top(); pq.pop();
L[0].m--, L[0].b += x;
}
cout << L[0].b << '\n';
}
