#include<bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("avx2")
#define ll long long
#define pii pair<int,int>
#define pll pair<ll,ll>
#define plx pair<ll,int>
#define f first
#define s second
#define pb push_back
#define all(x) x.begin(),x.end()
#define vi vector<int>
using namespace std;
const int mxn=3e5+5;
vector<int>g[mxn];
ll p[mxn],c[mxn],n;
priority_queue<int>q[mxn];
ll a[mxn]{0};ll b[mxn]{0};
void dfs(int u){
for(auto v:g[u]){
if(v>n)continue;
dfs(v);
while(a[v]>1){
a[v]--;
b[v]+=q[v].top();q[v].pop();
}
ll x=q[v].top();q[v].pop();
ll y=q[v].top();q[v].pop();
q[v].push(x+c[v]);q[v].push(y+c[v]);
b[v]-=c[v];
if(q[v].size()>q[u].size())swap(q[u],q[v]);
while(!q[v].empty())q[u].push(q[v].top()),q[v].pop();
a[u]+=a[v];b[u]+=b[v];
}
}
int main(){
ios_base::sync_with_stdio(0);cin.tie(0);
int m;cin>>n>>m;
for(int i=2;i<=n+m;i++)cin>>p[i]>>c[i],g[p[i]].pb(i);
for(int i=n+1;i<=n+m;i++){
q[p[i]].push(c[i]);q[p[i]].push(c[i]);
b[p[i]]-=c[i];a[p[i]]++;
}dfs(1);
while(a[1]>0){
a[1]--;b[1]+=q[1].top();q[1].pop();
}cout<<b[1];
}
