#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
#define pb push_back
#define ff first
#define ss second
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, m; cin>>n>>m;
int f = n + m;
vector<ll> p(f + 1);
vector<int> g[f + 1];
for (int i = 2; i <= n; i++){
int x, w; cin>>x>>w;
g[x].pb(i);
p[i] = p[x] + w;
}
vector<bool> d(f + 1);
for (int i = 1; i <= n; i++) d[i] = 1;
for (int i = n + 1; i <= f; i++){
int x, w; cin>>x>>w;
g[x].pb(i);
p[i] = p[x] + w;
if (x > n){
d[i] = 1;
}
}
vector<pll> t[f + 1];
for (int i = n + 1; i <= f; i++){
t[i].pb({p[i], 0});
}
function<void(int)> fill = [&](int v){
if (!d[v]) return;
vector<ll> s;
for (int i: g[v]){
fill(i);
for (auto p: t[i]){
s.pb(p.ff);
}
}
for (ll x: s){
ll sum = 0;
for (int i: g[v]){
if (t[i].empty()) continue;
ll mn = 1e18;
for (auto [a, b]: t[i]){
mn = min(mn, b + abs(a - x));
}
sum += mn;
}
t[v].pb({x, sum});
}
};
fill(1);
ll out = 1e18;
for (auto [x, y]: t[1]) out = min(out, y);
cout<<out<<"\n";
}
