#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i = a; i<int(b);++i)
#define all(v) v.begin(),v.end()
#define sz(v) v.size()
#define trav(a,c) for(auto a: c)
typedef long long ll;
typedef vector<ll> vi;
typedef pair<ll,ll> pii;
vector<vector<pii> > e;
vector<multiset<ll>> ms;
tuple<ll,ll> getCost(ll v){ //p1,p2,h
if(e[v].size()==0) {
ms.push_back(multiset<ll>({0,0}));
return make_tuple(ms.size()-1,0);
}
//ll slope = 0;
// vector<pii> events;
ll allPoints;
vector<ll> allChildpoints;
ll slope = 0;
ll costAllZero = 0;
rep(i,0,e[v].size()){
ll points;
ll costZero;
tie(points,costZero) = getCost(e[v][i].first);
//cout<<e[v][i].first<<": "<<endl;
//cout<<ms[ms.size()-1].size()<<endl;
//cout<<points->size()<<endl;
ll l1 = *prev(ms[points].end());
ll l2 = *prev(prev(ms[points].end()));
ms[points].erase(prev(ms[points].end()));
ms[points].erase(prev(ms[points].end()));
l1+=e[v][i].second;
l2+=e[v][i].second;
ms[points].insert(l1);
ms[points].insert(l2);
costZero += e[v][i].second;
slope -= ms[points].size()-1;
costAllZero += costZero;
allChildpoints.push_back(points);
/*cout<<"A"<<e[v][i].first<<endl;
cout<<allChildpoints.size()<<endl;
rep(i,0,allChildpoints.size()){
cout<<i<<": "<<endl;
cout<<ms[allChildpoints[0]].size()<<endl;
}*/
/*if(v==1){
cout<<e[v][i].first<<": "<<endl;
cout<<"costZero: "<<costZero<<endl;
trav(p,points){
cout<<p<<" ";
}
cout<<endl;
}*/
//allChildcosts.emplace(points,h);
}
ll mx = 0;
ll mxIndex = 0;
rep(i,0,allChildpoints.size()){
//cout<<i<<" "<<endl;
//cout<<allChildpoints.size()<<" "<<endl;
//cout<<ms[allChildpoints[i]].size()<<endl;
if(ms[allChildpoints[i]].size()>mx){
mx = ms[allChildpoints[i]].size();
mxIndex = i;
}
}
allPoints = allChildpoints[mxIndex];
rep(i,0,allChildpoints.size()){
if(i==mxIndex) continue;
trav(p,ms[allChildpoints[i]]) ms[allPoints].insert(p);
}
while(ms[allPoints].size()>-slope+1)
ms[allPoints].erase(prev(ms[allPoints].end()));
return make_tuple(allPoints,costAllZero);
}
int main(){
cin.sync_with_stdio(false);
ll n,m;
cin>>n>>m;
n+=m;
e.resize(n);
rep(i,1,n){
ll a = i;
ll b,c; cin>>b>>c;
e[b-1].push_back({a,c});
}
ll points;
ll costZero;
tie(points,costZero) = getCost(0);
ll last = 0;
ll ans = 1e18;
ll cost = costZero;
ll slope = -(ms[points].size()-1);
//cout<<"costZero: "<<costZero<<endl;
trav(p,ms[points]){
//cout<<p<<" ";
cost += slope*(p-last);
ans = min(ans,cost);
slope++;
last = p;
}
//cout<<endl;
cout<<ans<<endl;
}
