#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
//#include "temp.cpp"
#include <cstdio>
using namespace std;
#ifndef ONLINE_JUDGE
#define dbg(x) cerr << #x <<" "; print(x); cerr << endl;
#else
#define dbg(x)
#endif
#define sz(x) (int((x).size()))
#define len(x) (int)x.length()
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define clr(x) (x).clear()
#define uniq(x) x.resize(unique(all(x)) - x.begin());
#define blt __builtin_popcount
#define pb push_back
#define popf pop_front
#define popb pop_back
void print(long long t) {cerr << t;}
void print(int t) {cerr << t;}
void print(string t) {cerr << t;}
void print(char t) {cerr << t;}
void print(double t) {cerr << t;}
void print(long double t) {cerr << t;}
void print(unsigned long long t) {cerr << t;}
template <class T, class V> void print(pair <T, V> p);
template <class T> void print(vector <T> v);
template <class T> void print(set <T> v);
template <class T, class V> void print(map <T, V> v);
template <class T> void print(multiset <T> v);
template <class T, class V> void print(T v[],V n) {cerr << "["; for(int i = 0; i < n; i++) {print(v[i]); cerr << " "; } cerr << "]";}
template <class T, class V> void print(pair <T, V> p) {cerr << "{"; print(p.first); cerr << ","; print(p.second); cerr << "}";}
template <class T> void print(vector <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(set <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(multiset <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T, class V> void print(map <T, V> v) {cerr << "[ "; for (auto i : v) {print(i); cerr << " ";} cerr << "]";}
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
#define nl '\n'
// for grid problems
int dx[8] = {-1,0,1,0,1,-1,1,-1};
int dy[8] = {0,1,0,-1,1,1,-1,-1};
// lowest / (1 << 17) >= 1e5 / (1 << 18) >= 2e5 / (1 << 21) >= 1e6
void fastIO() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
}
// file in/out
void setIO(string str = "") {
fastIO();
if (str != "") {
freopen((str + ".in").c_str(), "r", stdin);
freopen((str + ".out").c_str(), "w", stdout);
}
}
// Indexed Set
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
const int N = 2e5 + 10, M = 3e2 + 10;
const long long inf = 1e15;
int n, m, out[N];
vector<pair<long long, long long>> adj[N];
long long dp[M][M];
void dfs(int node, int parent) {
if(!out[node]) {
for(int i = 0; i < M; i++) {
dp[node][i] = inf;
}
dp[node][0] = 0;
return;
}
for(auto i: adj[node]) {
if(i.first == parent) continue;
dfs(i.first, node);
for(int j = 0; j < M; j++) {
long long mini = INT64_MAX;
for(int k = 0; k <= j; k++) {
if(dp[i.first][k] == inf) {
continue;
}
mini = min(mini, dp[i.first][k] + abs(i.second - (j - k)));
}
dp[node][j] += mini;
}
}
}
void solve_() {
cin >> n >> m;
for(int i = 2; i <= n; i++) {
long long p, c; cin >> p >> c;
adj[i].push_back({p, c});
adj[p].push_back({i, c});
out[p]++;
}
for(int i = n + 1; i <= n + m; i++) {
long long p, c; cin >> p >> c;
adj[i].push_back({p, c});
adj[p].push_back({i, c});
out[p]++;
}
if(n == 1) {
long long answ = INT64_MAX;
for(auto i: adj[1]) {
long long ansi = 0;
for(auto j: adj[1]) {
ansi += abs(i.second - j.second);
}
answ = min(answ, ansi);
}
printf("%lld\n", answ);
return;
}
dfs(1, 0);
// dbg(dp[1][13])
long long answ = INT64_MAX;
for(int i = 0; i < M; i++) {
answ = min(answ, dp[1][i]);
}
printf("%lld\n", answ);
}
int main () {
setIO();
auto solve = [&](int test_case)-> void {
while(test_case--) {
solve_();
}
};
int test_cases = 1;
solve(test_cases);
return 0;
}
