#include <bits/stdc++.h>
using namespace std;
using ll = long long int;
const int MAX = (int) 3e5 + 10;
struct SlopeTrick{
struct Function{
ll a = 0,b = 0;
void operator +=(Function & ot){
a += ot.a;
b += ot.b;
}
};
priority_queue<ll> pts; // slope change
Function f; // last linear function
void arruma(int z){
if(pts.empty()){
f.a = 1;
f.b = -z;
pts.push(z);
pts.push(z);
return;
}
// os caras da inclinacao zero eu vou shiftar +z, dai os caras da esquerda eu vou shiftar +z e depois shiftar -z, ou seja, n vou fazer nada
ll lst=0;
while(f.a != 0){
ll x = pts.top();
pts.pop();
ll y = f.a*x + f.b;
f.a--;
f.b = y - f.a*x;
lst = x;
}
ll lst2 = pts.top();
pts.pop();
pts.push(lst2 + z);
pts.push(lst + z);
// considerar a nova inclinacao 1
f.a++;
f.b = f.b - f.a*(lst+z);
}
ll solve(){
while(f.a != 0){
ll x = pts.top();
pts.pop();
ll y = f.a*x + f.b;
f.a--;
f.b = y - f.a*x;
}
return f.b;
}
void show(){
priority_queue<ll> pq = pts;
Function g = f;
while(!pq.empty()){
ll x = pq.top();
pq.pop();
cout << x << ' ' << g.a << ' ' << g.b << endl;
ll y = g.a*x + g.b;
g.a--;
g.b = y - g.a*x;
}
cout << "-inf " << g.a << ' ' << g.b << endl;
}
};
vector<pair<int,int>> graph[MAX];
int rep[MAX];
SlopeTrick slp[MAX];
int get(int u){return rep[u] = rep[u] == u ? u : get(rep[u]);}
void merge(int u,int v){
u = get(u), v = get(v);
if(u == v) return;
if(slp[u].pts.size() < slp[v].pts.size()){
merge(v,u);
return;
}
auto & at = slp[u];
auto & ot = slp[v];
while(!ot.pts.empty()){
ll x = ot.pts.top();
ot.pts.pop();
at.pts.push(x);
}
at.f += ot.f;
rep[v] = u;
}
void solve(int u,int ant){
for(auto [v,z] : graph[u]){
if(v == ant) continue;
solve(v,u);
slp[get(v)].arruma(z);
merge(u,v);
}
// cout << u << ":\n";
// slp[get(u)].show();
}
void test(){
int n,m;
cin >> n >> m;
for(int i=1; i<=n+m; i++) rep[i] = i;
for(int i=2; i<=n+m; i++){
int x,z;
cin >> x >> z;
graph[x].push_back(make_pair(i,z));
graph[i].push_back(make_pair(x,z));
}
solve(1,1);
cout << slp[get(1)].solve() << '\n';
}
int main(){
ios::sync_with_stdio(false); cin.tie(nullptr);
int ttt_ = 1;
// cin >> ttt_;
while(ttt_--) test();
return 0;
}
