#include <bits/stdc++.h>
using namespace std;
#define ll long long
// const ll MOD = 998244353;
const ll MOD = 1e9 + 7;
const ll N = 3e5 + 2;
vector<vector<pair<int, int>>> edges(N);
vector<ll> dist(N, 0), ind(N), del(N, 0), a(N, 0), b(N, 0);
ll n, m;
vector<priority_queue<ll>> pq(N);
void merge(ll &node, ll child) {
int n1 = pq[node].size();
int n2 = pq[child].size();
if (!n1) {
node = child;
return;
}
if (n1 < n2) swap(node, child);
while (pq[child].size()) {
pq[node].push(pq[child].top());
pq[child].pop();
}
}
void dfs(int node, int parent) {
ll t1, t2, child = node, d;
for (auto it : edges[node]) {
child = it.first; d = it.second;
if (child == parent) continue;
if (n + 1 <= child && child <= n + m) {
pq[child].push(d); pq[child].push(d);
a[child] = 1;
b[child] = -d;
} else {
dfs(child, node);
b[child] -= d;
t1 = pq[ind[child]].top();
pq[ind[child]].pop();
t2 = pq[ind[child]].top();
pq[ind[child]].pop();
t1 += d; t2 += d;
pq[ind[child]].push(t2); pq[ind[child]].push(t1);
}
a[node] += a[child];
b[node] += b[child];
merge(ind[node], ind[child]);
}
while (a[node] > 1) {
b[node] += pq[ind[node]].top();
pq[ind[node]].pop();
a[node]--;
}
}
void solve() {
ll p, c, ans = 0;
cin >> n >> m;
for (int i = 2; i <= n + m; i++) {
cin >> p >> c;
edges[p].push_back(make_pair(i, c));
edges[i].push_back(make_pair(p, c));
}
for (int i = 1; i <= n + m; i++) ind[i] = i;
dfs(1, 0);
cout << a[1] * pq[ind[1]].top() + b[1] << "\n";
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
ll t;
t = 1;
// cin >> t;
while(t--) {
solve();
}
return 0;
}
