#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=1e6+999;
int n,m;
vector<pair<int,int> > to[N];
int val[N],dep[N]; 
int rt[N],son[N][2],cntnode;
ll k[N],b[N];
int merge(int x,int y){
	if(!x||!y) return x+y;
	if(val[x]<val[y]) swap(x,y);
	son[x][1]=merge(son[x][1],y);
	if(dep[son[x][1]]>dep[son[x][0]]) swap(son[x][0],son[x][1]);
	dep[x]=dep[son[x][1]]+1;
	return x;
}
void dfs(int u){
	int v,w;
	for(pair<int,int> now:to[u]){
		v=now.first; w=now.second;
		dfs(v); b[v]+=w;
		if(to[v].empty()) k[v]--;
		w=val[rt[v]]+w;
		rt[v]=merge(son[rt[v]][0],son[rt[v]][1]); 
		val[++cntnode]=w;
		rt[v]=merge(cntnode,rt[v]);
		val[++cntnode]=w;
		rt[v]=merge(cntnode,rt[v]);
		rt[u]=merge(rt[u],rt[v]);
		k[u]+=k[v]; b[u]+=b[v];
	}
	for(int i=0;i<to[u].size();i++)
		rt[u]=merge(son[rt[u]][0],son[rt[u]][1]);
	return;
}
int main(){
	std::ios::sync_with_stdio(false);
	cin.tie(0);
	cin>>n>>m; n+=m;
	int u,w;
	for(int i=2;i<=n;i++){
		cin>>u>>w;
		to[u].push_back(make_pair(i,w));
	}
	dfs(1); u=1;
	ll ans=b[1];
	ll ls=val[rt[u]],nk=1;
	rt[u]=merge(son[rt[u]][0],son[rt[u]][1]);
	while(rt[u]){
		ans-=(ls-val[rt[u]])*nk; nk++; ls=val[rt[u]];
		rt[u]=merge(son[rt[u]][0],son[rt[u]][1]);
	}
	ans-=ls*nk;
	cout<<ans;
	return 0;
}