#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("sse4")
using namespace std;
#define FOR(a,b) for(int a=0;a<b;a++)
#define F0R(a,b,c) for(int a = b; a<=c; a++)
#define f first
#define s second
#define m0(x) memset(x,0,sizeof(x))
#define all(x) x.begin(), x.end()
typedef pair<int,int> pi;
typedef long long ll;
typedef vector<int> vi;
typedef vector<pi> vpi;
struct hull{
priority_queue<ll> lhull;
priority_queue<ll,vector<ll>,greater<ll>> rhull;
ll height = 0;
void putpar(ll len){
if(lhull.empty()){
lhull.push(len);
rhull.push(len);
return;
}
ll a = lhull.top(); lhull.pop(); a += len;
lhull.push(a);
a = rhull.top();
while(!rhull.empty()) rhull.pop();
rhull.push(a+len);
}
void plu(ll num){
lhull.push(num);
ll a = lhull.top(); lhull.pop();
height += a-num;
rhull.push(a);
}
void pld(ll num){
rhull.push(num);
ll a = rhull.top(); rhull.pop();
height += num - a;
lhull.push(a);
}
void ins(ll num){
plu(num);
pld(num);
}
void combine(hull & other){
while(!other.lhull.empty()){
ll a = other.lhull.top();
other.lhull.pop();
pld(a);
}
while(!other.rhull.empty()){
ll a = other.rhull.top();
other.rhull.pop();
plu(a);
}
height += other.height;
}
};
vector<ll> children, root;
const int large = 3e5+1;
vi edges[large];
int dfs1(int child){
int ccnt = 1;
for(auto &a: edges[child]) ccnt += dfs1(a);
children[child] = ccnt;
return ccnt;
}
void dfs2(int child, hull &ans){
const int sz = edges[child].size();
vi &e = edges[child];
FOR(i,sz){
if(children[e[i]] > children[e[0]])
swap(e[i], e[0]);
}
if(sz != 0){
dfs2(e[0],ans);
}
F0R(i,1,sz-1){
hull cur;
dfs2(e[i],cur);
ans.combine(cur);
}
ans.putpar(root[child]);
}
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0);
int n,m; cin >> n >> m;
hull ans;
children.resize(n+m+1);
root.resize(n+m+1);
F0R(i,2,n+m){
int par;
cin >> par >> root[i];
edges[par].push_back(i);
}
dfs1(1);
dfs2(1,ans);
cout << ans.height << "\n";
return 0;
}
