#include<bits/stdc++.h>
#define newl '\n'
const int N = 3e5 + 10;
const int V = 1e7 + 10;
const long long INF = 1e18;
const long long M = 1e9 + 7;
long long f[N + 1],w[N + 1],bu[N + 1],shift[N + 1],n,m;
std::multiset<long long> slopel[N + 1],sloper[N + 1];
std::vector<int> adj[N + 1];
void readData(){
std::cin >> n >> m;
for(int i = 2;i <= n;++i){
long long p;
std::cin >> p >> w[i];
adj[p].emplace_back(i);
}
for(int i = 1;i <= m;++i){
long long p;
std::cin >> p >> w[n + i];
adj[p].emplace_back(n + i);
}
}
void add_dec(std::multiset<long long> &l,std::multiset<long long> &r,long long &b,long long x,long long left_shift){
if(x <= *r.begin()){
l.insert(x + left_shift);
}else{
long long x1 = *r.begin();
r.insert(x);
l.insert(x1 + left_shift);
b += x - x1;
r.erase(r.begin());
}
}
void add_inc(std::multiset<long long> &l,std::multiset<long long> &r,long long &b,long long x,long long left_shift){
if(x >= *l.rbegin() - left_shift){
r.insert(x);
}else{
long long x1 = *l.rbegin() - left_shift;
l.insert(x + left_shift);
r.insert(x1);
b += x1 - x;
l.erase(prev(l.end()));
}
}
void fix(int u){
while((int)sloper[u].size() > 1){
sloper[u].erase(prev(sloper[u].end()));
}
long long x = *prev(slopel[u].end());
slopel[u].erase(prev(slopel[u].end()));
slopel[u].insert(x + f[u]);
shift[u] += f[u];
}
///opt_y = 1 * x + b
///b = opt_y - x
///b = -opy_y + x
void get_size(int u = 1){
f[u] += w[u];
for(int v : adj[u]){
f[v] += f[u];
get_size(v);
}
}
void dfs(int u = 1){
int heavy = 0;
// if(u == )
for(int v : adj[u]){
dfs(v);
if(slopel[v].size() + sloper[v].size() > slopel[heavy].size() + sloper[heavy].size()){
heavy = v;
}
}
if(heavy == 0){
slopel[u].insert(f[u]);
sloper[u].insert(f[u]);
}else{
bu[u] = bu[heavy];
shift[u] = shift[heavy];
slopel[u].swap(slopel[heavy]);
sloper[u].swap(sloper[heavy]);
for(int v : adj[u]){
if(v == heavy){
continue;
}
for(long long val : slopel[v]){
long long x = val - shift[v];
add_dec(slopel[u],sloper[u],bu[u],x,shift[u]);
}
for(long long val : sloper[v]){
long long x = val;
add_inc(slopel[u],sloper[u],bu[u],x,shift[u]);
}
bu[u] += bu[v];
}
fix(u);
}
}
int main(){
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);std::cout.tie(nullptr);
readData();
get_size();
dfs();
std::cout << bu[1] << newl;
// for(int i = 1;i <= n + m;++i){
// std::cout << i << " " << bu[i] << newl;
// }
// std::cout << newl;
// for(long long t : slope[1]){
// std::cout << t << " ";
// }
// std::cout << w[2] << newl;
// std::cout << newl;
// for(int i = 1;i <= m;++i){
// std::cout << w[n + i] << " ";
// }
// std::cout << newl;
return 0;
}
