#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define FOR(i, l, r) for(int i = l; i <= r; i++)
#define FORD(i, l, r) for(int i = l; i >= r; i--)
#define db double
#define ldb long double
#define all_1(x) (x).begin() + 1, (x).end()
#define all(x) (x).begin(), (x).end()
#define ins insert
#define pb push_back
template<typename T>void debug_var(const T& var, const string& name){
cerr << name << ": " << var << "\n";
}
template<typename T>void debug_1d(const T& vt, const string& name){
if(vt.empty()){
cerr << name << " is empty!\n";
return;
}
FOR(i, 0, (int)vt.size() - 1){
cerr << name << "[" << i << "]: " << vt[i] << "\n";
}
}
const int N = 1e5 + 5;
const ll oo = 2e18;
int n;
ll w[N];
vector<pair<int, ll>> adj[N];
namespace sub2{
ll dp[305][305];
void dfs(int u, int p){
bool is_leaf = true;
for(auto [v, w] : adj[u]){
if(v == p)continue;
is_leaf = false;
dfs(v, u);
}
if(is_leaf){
dp[u][0] = 0;
FOR(i, 1, 300) dp[u][i] = oo;
return;
}
FOR(i, 1, 300) dp[u][i] = 0;
for(pair<int, ll> e : adj[u]){
int v = e.first;
ll w = e.second;
if(v == p) continue;
FOR(x, 0, 300){
ll min_cost = oo;
FOR(y, 0, x){
if(dp[v][y] != oo){
min_cost = min(min_cost, dp[v][y] + llabs(x - y - w));
}
}
dp[u][x] += min_cost;
}
}
}
void sol(){
dfs(1, -1);
ll ans = oo;
FOR(i, 0, 300) ans = min(ans, dp[1][i]);
cout << ans << "\n";
}
}
void solve(){
int m;
cin >> n >> m;
n += m;
FOR(i, 2, n){
int p;
ll c;
cin >> p >> c;
adj[p].pb({i, c});
adj[i].pb({p, c});
w[i] = c;
}
sub2::sol();
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int t = 1;
//cin >> t;
while(t--){
solve();
}
return 0;
}
