#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<ll> vi;
typedef pair<ll,ll> ii;
typedef vector<ii> vii;
typedef long double lld;
#define rep(i,a,b) for(ll i = a; i < b; i++)
#define per(i,a,b) for(ll i = a; i >= b; i--)
#define inf 1000000000000000000
#define all(x) x.begin(),x.end()
#define sz(x) (ll)(x).size()
#define trav(a,x) for(auto a : x)
ll n,m,p,c;
vii tree,_;
vector<vii> edges;
vi firstcase;
int main(){
cin >> n >> m;
edges.assign(n+m,_);
rep(i,0,n-1){
cin >> p >> c; p--;
tree.push_back(make_pair(p,c));
edges[i+1].push_back(make_pair(p,c));
edges[p].push_back(make_pair(i+1,c));
}
rep(i,n-1,m+n-1){
cin >> p >> c; p--;
tree.push_back(make_pair(p,c));
edges[i+1].push_back(make_pair(p,c));
edges[p].push_back(make_pair(i+1,c));
firstcase.push_back(c);
}
sort(all(firstcase));
ll res = 0;
rep(i,0,m) res += abs(firstcase[i]-firstcase[m/2]);
cout << res << endl;
}
