#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define endl '\n'
#define INF 1e9+7
#define all(x) x.begin(),x.end()
using namespace std;
using namespace __gnu_pbds;
using ll=long long;
using pii=pair<int,int>;
using ppi=pair<int,pii>;
using oset=tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update>;
template<typename T>
void _print(vector<T> x) {cerr<<"{"; for(auto e:x) cerr<<e<<","; cerr<<"}";}
void _print(pii x) {cerr<<"{"<<x.first<<","<<x.second<<"}";}
template<typename T>
void _print(T x) {cerr<<x;}
void dbg() {cerr<<endl;}
template<typename Head,typename... Tail>
void dbg(Head H,Tail... T) {
_print(H);
if(sizeof...(T)) cerr<<",";
else cerr<<"\"]";
dbg(T...);
}
#define debug(...) cerr<<"["<<#__VA_ARGS__<<"]:[\"",dbg(__VA_ARGS__)
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int mxn=310;
vector<pii> adj[mxn];
int dp[mxn][mxn];
int n,m;
int dfs(int u,int sum) {
if(dp[u][sum]!=-1) return dp[u][sum];
if(adj[u].empty()) return sum;
int res=0;
for(auto vw:adj[u]) {
int temp=INF;
int v=vw.first,w=vw.second;
for(int i=0;i<=sum;i++) {
temp=min(temp,abs(i-w)+dfs(v,sum-i));
}
res+=temp;
}
return dp[u][sum]=res;
}
int main () {
ios::sync_with_stdio(false); cin.tie(0);
cin>>n>>m;
memset(dp,-1,sizeof(dp));
for(int i=2;i<=n+m;i++) {
int u,w; cin>>u>>w;
adj[u].push_back({i,w});
}
int ans=INF;
for(int i=0;i<=300;i++) {
ans=min(ans,dfs(1,i));
// debug(i,dp[1][i]);
}
cout<<ans<<endl;
}
