#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int nx=3e5+5;
ll n, m, p, c, lz[nx], res[nx];
vector<pair<ll, ll>> d[nx];
priority_queue<ll> pql[nx];
priority_queue<ll, vector<ll>, greater<ll>> pqr[nx];
void dfs(int u)
{
if (u>n) return pql[u].push(0), pqr[u].push(0), void();
for (auto [v, w]:d[u])
{
dfs(v);
lz[v]+=w;
res[u]+=res[v];
ll upd[2]={pql[v].top()+lz[v], pqr[v].top()+lz[v]};
if (pql[u].empty())
{
pql[u].push(upd[0]);
pqr[u].push(upd[1]);
continue;
}
ll cl=pql[u].top(), cr=pqr[u].top();
if (cr<upd[0]) res[u]+=(upd[0]-cr);
else if (upd[1]<cl) res[u]+=cl-upd[1];
if (upd[0]>=pqr[u].top()) pqr[u].push(upd[0]);
else pql[u].push(upd[0]);
if (upd[1]>=pqr[u].top()) pqr[u].push(upd[1]);
else pql[u].push(upd[1]);
while (pql[u].size()>pqr[u].size()) pqr[u].push(pql[u].top()), pql[u].pop();
while (pqr[u].size()>pql[u].size()) pql[u].push(pqr[u].top()), pqr[u].pop();
//cout<<"size "<<pql[u].size()<<' '<<pqr[u].size()<<'\n';
}
//cout<<res[u]<<'\n';
/*
cout<<"debug : "<<u<<'\n';
cout<<"l : ";
priority_queue<ll> l=pql[u];
priority_queue<ll, vector<ll>, greater<ll>> r=pqr[u];
while (!l.empty()) cout<<l.top()+lz[u]<<' ', l.pop();
cout<<'\n';
cout<<"r : ";
while (!r.empty()) cout<<r.top()+lz[u]<<' ', r.pop();
cout<<'\n';
cout<<"res "<<u<<' '<<res[u]<<'\n';*/
}
int main()
{
cin.tie(NULL)->sync_with_stdio(false);
cin>>n>>m;
for (int i=2; i<=n+m; i++) cin>>p>>c, d[p].push_back({i, c});
dfs(1);
cout<<res[1];
}
/*
*/
