#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#pragma optimize("unroll-loops")
#define fast ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define all(x) x.begin(), x.end()
#define rll(x) x.rbegin(), x.rend()
#define COMP(x) x.erase(unique(all(x)), x.end())
#define MOD 1000000007
#define MOD2 998244353
#define sz(x) (ll)x.size()
typedef __int128_t lll;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll,ll> pll;
typedef pair<ll, pll> PP;
const ll Lnf = 2e18;
ll n, m;
vector<array<ll,2>> adj[303030];
ll w[303030]; //부모 간선의 가중치
ll num[303030];
priority_queue<ll> pq[303030];
ll b[303030];
void dfs(ll x){
ll a = 0;
pq[num[x]].push(0);
pq[num[x]].push(0);
for(auto [next,w] : adj[x]){
dfs(next);
a++;
b[x] += b[next];
if(sz(pq[num[x]]) < sz(pq[num[next]]))swap(num[x],num[next]);
while(sz(pq[num[next]]))pq[num[x]].push(pq[num[next]].top()), pq[num[next]].pop();
}
while(a>1){
a--;
b[x] += pq[num[x]].top(); pq[num[x]].pop();
}
// cout<<x<<" "<<pq[num[x]].top()<<" "<<b[x]<<endl;
ll r = pq[num[x]].top(); pq[num[x]].pop();
ll l = pq[num[x]].top(); pq[num[x]].pop();
pq[num[x]].push(l+w[x]); pq[num[x]].push(r+w[x]);
b[x] -= w[x];
if(x==1)cout<<pq[num[x]].top() + b[x];
// cout<<x<<" "<<pq[num[x]].top()<<" "<<b[x]<<endl;
}
int main(){
fast;
cin>>n>>m;
for(int i = 1 ; i <= n+m ; i++)num[i]=i;
for(int i = 2 ; i <= n+m ; i++){
ll p; cin>>p>>w[i];
adj[p].push_back({i,w[i]});
}
dfs(1);
}
