#include <bits/stdc++.h>
using namespace std;
using ll=long long;
const int __=3e5+1;
int n, m, par[__];
ll d[__], ans;
priority_queue<ll> a[__];
priority_queue<ll, vector<ll>, greater<ll>> b[__];
vector<pair<int,ll>> g[__];
int find(int u) {
if (par[u]==u) return u;
return par[u]=find(par[u]);
}
void merge(int u, int v) {
u = find(u), v = find(v);
if (u==v) return;
if (a[u].size()>a[v].size()) swap(u, v);
ll o = d[u]-d[v];
while (a[u].size()) {
ll x = a[u].top();
a[u].pop();
a[v].push(x+o);
}
par[u] = v;
}
void add(int u, ll r) {
int uu = u;
u = find(u);
ll x = d[u]+a[u].top();
if (r<x) {
a[u].push(r-d[u]);
a[u].pop();
b[uu].push(x);
ans += x-r;
} else {
b[uu].push(r);
}
}
ll dfs(int i, int p) {
vector<pair<ll, int>> v;
for (auto [j, x]: g[i])
if (j!=p) v.emplace_back(dfs(j, i), j);
sort(v.begin(), v.end(), greater<pair<ll, int>>());
for (auto [r, j]: v) {
if (par[i]==i) {
par[i] = j;
b[i].push(r);
} else {
add(i, r);
merge(i, j);
}
}
int pi = find(i);
ll r = b[i].size()? b[i].top() + d[i] : d[i];
ll l = a[pi].size()? a[pi].top() + d[pi] + d[i] : d[i];
if (a[pi].size()) a[pi].pop();
a[pi].push(l-d[pi]);
return r;
}
void init(int i, int p) {
for (auto [j, c]: g[i])
if (j!=p) {
d[j] = c;
init(j, i);
}
}
int main() {
scanf("%d%d", &n, &m);
for (int i=1; i<=n+m; ++i) par[i] = i;
for (int i=2; i<=n+m; ++i) {
int p; ll c;
scanf("%d%lld", &p, &c);
g[i].emplace_back(p, c);
g[p].emplace_back(i, c);
}
init(1, 0);
dfs(1, 0);
printf("%lld\n", ans);
}
