#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();
}
}t[300005];
int p[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];
for(int i=n+m;i>n;--i) t[p[i]].insert(c[i]);
for(int i=n;i>1;--i){
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);
t[p[i]]+=t[i];
t[i].clear();
}
cout<<t[1].mn;
}
