#include <bits/stdc++.h>
using namespace std;
#define REP(i,n) for(int (i)=0;(i)<(int)(n);(i)++)
#define REPO(i,n) for(int (i)=1; (i)<=(int)(n); (i)++)
#define SZ(v) ((int)(v).size())
#define ALL(v) (v).begin(),(v).end()
#define one first
#define two second
typedef long long ll;
typedef pair<int, int> pi;
const int INF = 0x3f2f1f0f;
const ll LINF = 1ll * INF * INF;
const int MAX_N = 3e5 + 100;
int N, M, S[MAX_N], P[MAX_N], C[MAX_N];
vector<pi> Ed[MAX_N];
struct SL {
priority_queue<ll> Ls;
priority_queue<ll, vector<ll>, greater<ll> > Rs;
ll baseL, baseR, ans;
SL() {
baseL = baseR = ans = 0;
while(!Ls.empty()) Ls.pop();
while(!Rs.empty()) Ls.pop();
}
void update() {
while(Ls.top()+baseL > Rs.top()+baseR) {
ll a = Ls.top()+baseL;
ll b = Rs.top()+baseR;
ans += a-b;
Ls.pop(); Rs.pop();
Ls.push(b-baseL); Rs.push(a-baseR);
}
}
void add(ll l, ll r) {
Ls.push(l-baseL), Rs.push(r-baseR);
update();
}
void add(SL &o) {
ans += o.ans;
while(!o.Ls.empty()) Ls.push(o.Ls.top() + o.baseL - baseL), o.Ls.pop();
while(!o.Rs.empty()) Rs.push(o.Rs.top() + o.baseR - baseR), o.Rs.pop();
update();
}
void addLine(int b) {
baseR += b; baseL += 0;
ll l = Ls.top(), r = Rs.top();
Ls.pop();
Ls.push(l+b);
while(!Rs.empty()) Rs.pop();
Rs.push(r);
update();
}
};
vector<SL> Ss; int Ix[MAX_N];
void dfs(int v, int p) {
S[v] = 1;
int maxV = -1, ix = -1;
for(pi &e : Ed[v]) {
int w, c; tie(w, c) = e;
if(w == p) continue;
dfs(w, v);
S[v] += S[w];
if(maxV < S[w]) maxV = S[w], ix = w;
}
if(ix == -1) {
int c = C[v];
SL node; node.add(c, c);
Ix[v] = Ss.size();
Ss.push_back(node);
} else {
Ix[v] = Ix[ix];
for(pi &e : Ed[v]) {
int w, c; tie(w, c) = e;
if(w == p || w == ix) continue;
Ss[Ix[v]].add(Ss[Ix[w]]);
}
Ss[Ix[v]].addLine(C[v]);
}
}
int main() {
cin >> N >> M; N += M;
for(int i=2; i<=N; i++) {
int p, c; scanf("%d%d", &p, &c);
P[i] = p; C[i] = c;
Ed[i].push_back(pi(p, c));
Ed[p].push_back(pi(i, c));
}
dfs(1, 0);
printf("%lld\n", Ss[Ix[1]].ans);
return 0;
}
