#include<bits/stdc++.h>
#pragma optimize ("g",on)
#pragma GCC optimize ("inline")
#pragma GCC optimize ("Ofast")
#pragma GCC optimize ("unroll-loops")
#pragma GCC optimize ("03")
#pragma GCC target ("sse,sse2,sse3,ssse3,sse4,popcnt,abm,avx2,mmx,fma,avx,tune=native")
//01001101 01100001 01101011 01101000 01100001 01100111 01100001 01111001
using namespace std;
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define ll long long
#define pb push_back
#define sz(a) a.size()
#define nl '\n'
#define popb pop_back()
#define ld double
#define ull unsigned long long
#define ff first
#define ss second
#define fix fixed << setprecision
#define pii pair<int, int>
#define E exit (0)
#define int long long
const int inf = 1e15, N = 501, mod = 998244353;
double eps = 1e-6;
vector<pii> dir = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
vector<pii> adj[N];
int cnt[N], dp[N][N];
int n, m;
void calc(int u) {
if (u > n) {
cnt[u]++;
}
for (auto to: adj[u]) {
calc(to.ff);
cnt[u] += cnt[to.ff];
}
}
void dfs(int u) {
if (u > n) {
for (int val = 0; val <= 300; val++) dp[u][val] = val;
return;
}
for (auto to: adj[u]) {
if (cnt[to.ff]) {
dfs(to.ff);
}
}
for (int val = 0; val <= 300; val++) {
dp[u][val] = 0;
for (auto to: adj[u]) {
if (!cnt[to.ff]) continue;
int mn = inf;
for (int c = 0; c <= val; c++) {
mn = min(mn, dp[to.ff][val - c] + abs(to.ss - c));
}
dp[u][val] += mn;
}
}
}
main() {
//freopen("F.in", "r", stdin);
//freopen("F.out", "w", stdout);
ios_base::sync_with_stdio(NULL);
cin.tie(NULL);
cin >> n >> m;
vector<int> s;
for (int i = 2; i <= n + m; i++) {
int p, c;
cin >> p >> c;
s.pb(c);
adj[p].pb({i, c});
}
if (n == 1) {
sort(all(s));
int val = s[sz(s) / 2], ans = 0;
for (auto x: s) ans += abs(x - val);
cout << ans;
return 0;
}
calc(1);
dfs(1);
int ans = inf;
for (int val = 0; val <= 300; val++) ans = min(ans, dp[1][val]);
cout << ans;
}
