#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
using ll=long long;
struct A{
multiset<ll> L,R;
ll mn;
A():mn(0){}
void insert(ll x){
if(L.empty()) L.emplace(x), R.emplace(x);
else if(x<*L.rbegin()){
mn+=*L.rbegin()-x;
L.emplace(x), L.emplace(x);
R.emplace(*L.rbegin()), L.erase(prev(L.end()));
}
else if(x>*R.begin()){
mn+=x-*R.begin();
R.emplace(x), R.emplace(x);
L.emplace(*R.begin()), R.erase(R.begin());
}
else L.emplace(x), R.emplace(x);
}
A& operator+=(A o){
if(L.size()<o.L.size()) swap(*this,o);
for(auto &e:o.L){
if(e<*R.begin()) L.emplace(e);
else{
mn+=e-*R.begin();
R.emplace(e), L.emplace(*R.begin()), R.erase(R.begin());
}
}
for(auto &e:o.R){
if(e>*L.rbegin()) R.emplace(e);
else{
mn+=*L.rbegin()-e;
L.emplace(e), R.emplace(*L.rbegin()), L.erase(prev(L.end()));
}
}
mn+=o.mn;
return *this;
}
void clear(){L.clear(),R.clear();}
int sz(){return L.size()+R.size();}
}t[300005];
vector<int> adj[300005];
int p[300005],big[300005];
ll c[300005];
int main(){
ios::sync_with_stdio(false); cin.tie(0);
int n,m; cin>>n>>m;
for(int i=2;i<=n+m;++i) cin>>p[i]>>c[i], adj[p[i]].emplace_back(i);
for(int i=n+m;i>n;--i) t[i].insert(0);
for(int i=n+m;i>=1;--i){
if(i<=n) swap(t[i],t[big[i]]);
for(auto &v:adj[i]){
if(v==big[i]) continue;
t[i]+=t[v];
t[v].clear();
}
if(i==1) break;
while(t[i].R.size()>1){
auto itr=prev(t[i].R.end());
t[i].R.erase(itr);
}
auto itr1=prev(t[i].L.end()), itr2=t[i].R.begin();
t[i].L.emplace(*itr1+c[i]), t[i].L.erase(itr1);
t[i].R.emplace(*itr2+c[i]), t[i].R.erase(itr2);
if(!big[p[i]] || t[big[p[i]]].sz()<t[i].sz()) big[p[i]]=i;
}
cout<<t[1].mn;
}
