#include <bits/stdc++.h>
using namespace std;
//st>=n are explosives
int n,m;
#define int long long
struct slopeTrick{
priority_queue<int>pri;
int mn;
int lazy;
void shift(int x){
lazy+=x;
}
void push(int x){
pri.push(x-lazy);
}
int top(){
return pri.top()+lazy;
}
void pop(){
pri.pop();
}
int size(){
return pri.size();
}
void printer(){
vector<int>temp;
while(size()){
temp.push_back(top());
pop();
}
reverse(temp.begin(),temp.end());
for(int i : temp){
cout << i << " ";
push(i);
}
cout << "\n";
}
};
const int mxn = 3e5+5;
slopeTrick slopes[mxn];
void dfs(int st, vector<array<int,2>>g[]){
for(array<int,2>a:g[st]){
dfs(a[0],g);
}
slopes[st].mn=0;
slopes[st].lazy=0;
if(st>=n){
slopes[st].push(0);
slopes[st].push(0);
}
for(array<int,2>a:g[st]){
if(slopes[a[0]].size()==0){
continue;
}
///merge slopes[a[0]],slopes[st] into slopes[st];
///first shift slopes[a[0]]
slopes[a[0]].shift(a[1]);
int A = slopes[a[0]].top();
slopes[a[0]].pop();
int B = slopes[a[0]].top();
slopes[a[0]].pop();
slopes[a[0]].shift(-a[1]);
slopes[a[0]].push(A);
slopes[a[0]].push(B);
///slopes shifted change of this edge accounted for now must merge.
if(slopes[a[0]].size()>slopes[st].size()){
swap(slopes[a[0]],slopes[st]);
}
if(slopes[a[0]].size()==0)
continue;
slopes[st].mn+=slopes[a[0]].mn;
///first one first
if(slopes[a[0]].top()>=slopes[st].top()){
slopes[a[0]].pop();
//nothing happens
}
else{
///shenangians
slopes[st].push(slopes[a[0]].top());
slopes[st].pop();
slopes[st].mn+=slopes[st].top()-slopes[a[0]].top();
slopes[a[0]].pop();
}
//first one done now others
while(slopes[a[0]].size()){
if(slopes[a[0]].top()>=slopes[st].top()){
slopes[st].mn+=slopes[a[0]].top()-slopes[st].top();
slopes[st].push(slopes[a[0]].top());
slopes[a[0]].pop();
}
else{
slopes[st].push(slopes[a[0]].top());
slopes[a[0]].pop();
}
}
}
}
signed main(){
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> m;
vector<array<int,2>>g[n+m];
for(int i = 1;i<n;i++){
int p,c;
cin >> p >> c;
p--;
g[p].push_back({i,c});
}
for(int i = 0;i<m;i++){
int p,c;
cin >> p >> c;
p--;
g[p].push_back({i+n,c});
}
dfs(0,g);
cout << slopes[0].mn;
return 0;
}
