#include <bits/stdc++.h>
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
using namespace std;
typedef long long ll;
const int MAXN = (int)3e5 + 5;
ll h0[MAXN], a0[MAXN];
priority_queue<ll> S[MAXN];
int par[MAXN], edge_len[MAXN];
vector<int> adj[MAXN];
int n, m;
int main() {
cin >> n >> m;
for (int i = 2; i <= n + m; i++) {
cin >> par[i] >> edge_len[i];
adj[par[i]].push_back(i);
}
for (int v = n + m; v > n; v--) {
h0[v] = edge_len[v];
a0[v] = -1;
S[v].push(edge_len[v]);
S[v].push(edge_len[v]);
}
for (int v = n; v > 0; v--) {
for (int to : adj[v]) {
h0[v] += h0[to];
a0[v] += a0[to];
if (sz(S[to]) > sz(S[v])) {
S[v].swap(S[to]);
}
while (!S[to].empty()) {
S[v].push(S[to].top());
S[to].pop();
}
}
while (!S[v].empty() && a0[v] + sz(S[v]) > 1) {
S[v].pop();
}
h0[v] += edge_len[v];
ll P = S[v].top();
S[v].pop();
ll Q = S[v].top();
S[v].pop();
S[v].push(Q + edge_len[v]);
S[v].push(P + edge_len[v]);
}
vector<ll> slopes;
while (!S[1].empty()) {
slopes.push_back(S[1].top());
S[1].pop();
}
reverse(all(slopes));
ll val = h0[1], slope = a0[1], pos = 0;
for (ll pt : slopes) {
val += (pt - pos) * slope;
pos = pt;
slope++;
if (slope == 0) break;
}
cout << val << endl;
return 0;
}
