#include <bits/stdc++.h>
#define fi first
#define se second
#define pb push_back
#define REP(i,o,n) for(auto i=o;i<n;i++)
using namespace std;
pair<long long,pair<long long,long long>> dp[200100];
long long getval(pair<long long,pair<long long,long long>> f, long long x){
if(f.se.se < x)return x+f.fi-f.se.se;
if(f.se.fi < x)return f.fi;
return f.se.fi+f.fi-x;
}
vector<long long> child[200100];
long long par[200100];
void dfs(long long node){
if(!child[node].size()){
dp[node]={0,{par[node],par[node]}};
return;
}
vector<long long> v;
for(auto i:child[node])dfs(i),v.pb(dp[i].se.fi),v.pb(dp[i].se.se);
sort(v.begin(),v.end());
dp[node].se = {v[child[node].size()-1],v[child[node].size()]};
dp[node].fi = 0;
for(auto i:child[node])dp[node].fi += getval(dp[i],dp[node].se.fi);
dp[node].se.fi += par[node];
dp[node].se.se += par[node];
}
signed main() {
long long n,m;cin>>n>>m;
REP(i,2,n+m+1){
long long p;cin>>p;
cin>>par[i];
child[p].pb(i);
}
dfs(1);
cout<<dp[1].fi;
}
