/*
ID: ekrem
LANG: C++
TASK: Fireworks
*/
#include <algorithm>
#include <iostream>
#include <cassert>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <iomanip>
#include <numeric>
#include <cstdio>
#include <string>
#include <vector>
#include <cmath>
#include <ctime>
#include <queue>
#include <stack>
#include <map>
#include <set>
using namespace std;
#define foreach(kk,gg) for(__typeof(gg.begin())kk=gg.begin();kk!=gg.end();kk++)
#define dbgs(x) cerr << (#x) << " --> " << (x) << ' '
#define dbg(x) cerr << (#x) << " --> " << (x) << endl
#define FOR(ii,aa,bb) for(int ii=aa;ii<=bb;ii++)
#define ROF(ii,aa,bb) for(int ii=aa;ii>=bb;ii--)
#define SET(a, b) memset(a, b, sizeof a)
#define heap priority_queue
#define orta (bas+son>>1)
#define endll puts("")
#define mp make_pair
#define pb push_back
#define sag (k+k+1)
#define sol (k+k)
#define endl '\n'
#define nd second
#define st first
#define y1 ekrem
#define y2 merke
typedef int don;
#define int long long int
inline int read(){int x;scanf(" %lld",&x);return x;}
typedef pair < int , int > ii;
typedef vector < int > vi;
typedef vector < ii > vii;
const int inf = 1e9 + 7;
const int linf = 1e18 + 7;
const int N = 1e6 + 5;
int n, m, p[N], c[N], a[N], b[N];
heap < int > h[N];
void ekle(int par, int coc){
a[par] += a[coc];
b[par] += b[coc];
heap < int > x;
if(h[par].size() > h[coc].size()){
x = h[par];
while(!h[coc].empty()){
int t = h[coc].top();h[coc].pop();
x.push(t);
}
} else{
x = h[coc];
while(!h[par].empty()){
int t = h[par].top();h[par].pop();
x.push(t);
}
}
h[par] = x;
}
don main(){
// freopen("input.in", "r", stdin);freopen("input.out", "w", stdout);
n = read();
m = read();
FOR(i, 2, n + m){
p[i] = read();
c[i] = read();
}
ROF(i, n + m, n + 1){//Yapraklar
a[i] = 1;
b[i] = -c[i];
h[i].push(c[i]);
h[i].push(c[i]);
ekle(p[i], i);
}
ROF(i, n, 2){
while(a[i] > 1){
a[i]--;
b[i] += h[i].top();h[i].pop();
}
int bir = h[i].top();h[i].pop();
int iki = h[i].top();h[i].pop();
h[i].push(bir + c[i]);
h[i].push(iki + c[i]);
b[i] -= c[i];//Bu ne
ekle(p[i], i);
}
while(a[1] > 0){
a[1]--;
b[1] += h[1].top();h[1].pop();
}
cout << b[1] << endl;
return 0;
}
