//叫んで 藻掻もがいて 瞼まぶたを腫らしても
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll , ll> pii;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int maxn = 300 + 10;
const ll mod = 1e9+7;
#define pb push_back
#define endl '\n'
#define dokme(x) cout << x , exit(0)
#define ms(x , y) memset(x , y , sizeof x)
ll pw(ll a, ll b, ll md = mod){ll res = 1;while(b){if(b&1){res=(a*res)%md;}a=(a*a)%md;b>>=1;}return(res);}
int n , m;
vector < pii > adj[maxn];
int dp[maxn][maxn];
int solve(int v){
if(adj[v].size() == 0){
for(int i = 0 ; i < maxn ; i ++)dp[v][i] = 1e6;
dp[v][0] = 0;
return 0;
}
for(auto u : adj[v])
solve(u.first);
for(int i = 0 ; i < maxn ; i ++){
for(auto uw : adj[v]){
int u = uw.first , w = uw.second;
int mn = 1e6;
for(int j = 0 ; j <= i ; j ++)
mn = min(mn , abs(w - j) + dp[u][i - j]);
dp[v][i] += mn;
}
}
return *min_element(dp[v] , dp[v] + maxn);
}
int32_t main(){
ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
cin >> n >> m;
n += m;
for(int i = 2 ; i <= n ; i ++){
int v , w;
cin >> v >> w;
adj[v].pb({i , w});
}
cout << solve(1);
return(0);
}
