#include<bits/stdc++.h>
#pragma GCC optimize("unroll-loops,no-stack-protector,Ofast")
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> pll;
const ll MOD=1e9+7;
const ll MOD2=998244353;
const ll N=1e6+5;
const ld pi=acos(-1);
const ll INF=(1LL<<60);
#define SQ(i) ((i)*(i))
#define REP(i,n) for(ll i=0;i<n;i++)
#define REP1(i,n) for(ll i=1;i<=n;i++)
#define pb push_back
#define mp make_pair
#define X first
#define Y second
#define setp setprecision
#define lwb lower_bound
#define SZ(_a) (ll)_a.size()
struct data{
ll a,b;
priority_queue<ll> *pq;
data operator+(data B){
data s;
s.a=a+B.a;
s.b=b+B.b;
if(pq->size()>B.pq->size()){
s.pq=pq;
while(!B.pq->empty()){
s.pq->push(B.pq->top());
B.pq->pop();
}
}else{
s.pq=B.pq;
while(!pq->empty()){
s.pq->push(pq->top());
pq->pop();
}
}
return s;
}
}d[N];
ll n,m,p[N],c[N];
int main(){
ios_base::sync_with_stdio(0);cin.tie(0);
cin>>n>>m;
for(int i=2;i<=n+m;i++){
cin>>p[i]>>c[i];
}
REP1(i,n+m)d[i].a=d[i].b=0,d[i].pq=new priority_queue<ll>;
for(int i=n+m;i>n;i--){
d[i].a=1;
d[i].b=-c[i];
d[i].pq->push(c[i]);
d[i].pq->push(c[i]);
d[p[i]]=d[p[i]]+d[i];
}
for(int i=n;i>1;i--){
while(d[i].a>1){
--d[i].a;
d[i].b+=d[i].pq->top();
d[i].pq->pop();
}
ll tmpa=d[i].pq->top();d[i].pq->pop();
ll tmpb=d[i].pq->top();d[i].pq->pop();
d[i].pq->push(tmpa+c[i]);
d[i].pq->push(tmpb+c[i]);
d[i].b-=c[i];
d[p[i]]=d[p[i]]+d[i];
}
while(d[1].a>0){
--d[1].a;
d[1].b+=d[1].pq->top();
d[1].pq->pop();
}
cout<<d[1].b<<"\n";
return 0;
}
