#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define ll long long
#define ld long double
const int N=5050;
const ll inf=1e16;
void chmn(ll &x,ll y){x=min(x,y);}
void chmx(ll &x,ll y){x=max(x,y);}
vector<pair<int,ll>>E[N];
ll Val[N],Val1[N];
int n,m;
void DFS1(int u){
for(auto [i,w]:E[u]){
Val1[i]=Val[i]=Val[u]+w;
DFS1(i);
}
}
struct SegTree{
int root,nc,lc[2*N],rc[2*N];ll mn[2*N];
SegTree(){mn[0]=inf;}
void Update(int &c,int ss,int se,int qind,ll x){
if(!c)c=++nc;
if(ss==se){mn[c]=x;return;}
int mid=ss+se>>1;
if(qind<=mid) Update(lc[c],ss,mid,qind,x);
else Update(rc[c],mid+1,se,qind,x);
mn[c]=min(mn[lc[c]],mn[rc[c]]);
}
ll Get(int c,int ss,int se,int qs,int qe){
if(qs>qe||qe<ss||se<qs)return inf;
if(qs<=ss&&se<=qe)return mn[c];
int mid=ss+se>>1;return min(Get(lc[c],ss,mid,qs,qe),Get(rc[c],mid+1,se,qs,qe));
}
}ST[2];
ll dp[N][N];
void DFS(int u){
if(E[u].empty()){
for(int x=1;x<=n;x++) if(Val[x]!=Val1[u]) dp[u][x]=inf;
return;
}
for(auto [c,w]:E[u]) DFS(c);
for(auto [c,w]:E[u]){
for(int y=1;y<=n;y++){
ST[0].Update(ST[0].root,1,n,y,dp[c][y]-Val[y]);
ST[1].Update(ST[1].root,1,n,y,dp[c][y]+Val[y]);
}
for(int x=1;x<=n;x++){
ll mn=inf;
int lb=upper_bound(Val+1,Val+n+1,Val[x])-Val-1;
int ub=upper_bound(Val+1,Val+n+1,Val[x]+w)-Val-1;
/*for(int i=1;i<=n;i++) printf("%lld ",Val[i]);printf("\n");
printf("%lld: %i\n",Val[x],lb);
printf("%lld: %i\n",Val[x]+w,ub);*/
if(0<lb) chmn(mn,ST[0].Get(ST[0].root,1,n,1,lb)+Val[x]);
if(lb<ub) chmn(mn,ST[1].Get(ST[1].root,1,n,lb+1,ub)-Val[x]);
/*for(int y=1;y<=n;y++){
if(Val[y]-w<=Val[x]) chmn(mn,dp[c][y]+abs(Val[x]-Val[y]));
}*/
dp[u][x]+=mn;
chmn(dp[u][x],inf);
}
}
}
int main(){
scanf("%i%i",&n,&m);n+=m;
for(int i=2;i<=n;i++){
int p;ll w;scanf("%i%lld",&p,&w);
E[p].pb({i,w});
}
DFS1(1);
sort(Val+1,Val+1+n);
DFS(1);
ll res=inf;
for(int i=1;i<=n;i++) chmn(res,dp[1][i]);
printf("%lld\n",res);
return 0;
}
