#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
#define int long long
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pii> vii;
typedef vector<bool> vb;
typedef deque<int> di;
typedef deque<pii> dii;
typedef tree<pii,null_type,less<pii>,rb_tree_tag,
tree_order_statistics_node_update> oset;
#define fi first
#define se second
#define pb push_back
#define pf push_front
#define mid (l+r)/2
#define all(x) x.begin(),x.end()
#define FOR(i,a) for(int i=0;i<(a);i++)
#define FORE(i,a,b) for(int i=(a);i<(b);i++)
#define cont(x) for(auto el:x) cout<<el<<' ';cout<<endl;
#define contp(x) for(auto el:x) cout<<el.fi<<'-'<<el.se<<' ';cout<<endl;
#define sp <<" "<<
#define DEBUG(x) cout<<(#x) sp x<<endl
#define carp(a,b) (((a%MOD)*(b%MOD))%MOD)
#define topla(a,b) (((a%MOD)+(b%MOD))%MOD)
const int INF=1e18;
const int MAXN=5e3+5;
const int MOD=1e9+7;
int n,m;
bool mark[MAXN];
int dp[MAXN][MAXN]; //d[i][j] --> i. nodea mesafe jkenki min cost
vii adj[MAXN];
void dfs(int nd,int ata){
for(auto [kom,cost]:adj[nd]){
if(kom==ata) continue;
dfs(kom,nd);
}
if(mark[nd]){
//DEBUG(nd);
dp[nd][0]=0;
return;
}
FOR(j,301){
//bana olan mesafe j olsun
for(auto [kom,cost]:adj[nd]){
if(kom==ata) continue;
int mn=INF;
FOR(k,j+1){
//komşuya mesafe k olsun
if(dp[kom][k]==INF) continue;
int ekle=abs(cost-(j-k));
mn=min(mn,dp[kom][k]+ekle);
}
//cout<<"here" sp mn sp nd sp kom sp j<<endl;
if(mn==INF){
dp[nd][j]=INF;
break;
}
else{
if(dp[nd][j]==INF) dp[nd][j]=0;
dp[nd][j]+=mn;
}
}
}
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
multiset<int> s;
cin>>n>>m;
FORE(i,1,n){
int a=i+1;
int b,c;
cin>>b>>c;
adj[a].pb({b,c});
adj[b].pb({a,c});
s.insert(c);
}
FORE(i,1,m+1){
int a=n+i;
int b,c;
cin>>b>>c;
adj[a].pb({b,c});
adj[b].pb({a,c});
mark[a]=true;
s.insert(c);
}
if(n==1){
vi vec;
for(auto el:s) vec.pb(el);
int sz=vec.size();
int med=vec[sz/2];
int ans=0;
for(auto el:vec){
ans+=abs(el-med);
}
cout<<ans<<endl;
}
else{
FORE(i,1,n+m+1){
FOR(j,301){
dp[i][j]=INF;
}
}
dfs(1,-1);
int ans=INF;
FOR(j,301){
ans=min(ans,dp[1][j]);
}
cout<<ans<<endl;
}
}
