#include <bits/stdc++.h>
#define fi first
#define se second
#define all(v) v.begin(), v.end()
#define eb emplace_back
#define em emplace
using namespace std;
typedef long long ll;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;
const int INF = 1 << 30;
const ll LINF = 1LL << 62;
const int MAX = 303030;
ll ans = 0;
struct node{
priority_queue <ll> L;
priority_queue <ll, vector <ll>, greater <ll> > R;
int sz = 0;
void merge(node &X) {
if(X.sz == 0) return;
sz += X.sz;
while(!X.L.empty()) {
ll temp = X.L.top();
X.L.pop();
if(temp > R.top()){
ans += temp - R.top();
L.em(R.top()); R.pop();
R.em(temp);
}
else L.em(temp);
}
while(!X.R.empty()) {
ll temp = X.R.top();
X.R.pop();
if(temp < L.top()){
ans += L.top() - temp;
R.em(L.top()); L.pop();
L.em(temp);
}
else R.em(temp);
}
}
void modify(ll val) {
ll Rt = 0, Lt = 0;
if(!R.empty()) Rt = R.top();
if(!L.empty()) Lt = L.top();
while(!R.empty()) R.pop(), sz--;
R.push(Rt + val);
L.push(Lt + val);
sz += 2;
}
} dp[MAX];
int p[MAX], idx[MAX];
ll c[MAX];
int main() {
ios::sync_with_stdio(false); cin.tie(0);
int n, m;
cin >> n >> m;
for(int i = 2; i <= n + m; i++) {
cin >> p[i] >> c[i];
idx[i] = i;
}
for(int i = n + m; i > 1; i--) {
dp[idx[i]].modify(c[i]);
if(dp[idx[p[i]]].sz < dp[idx[i]].sz) {
dp[idx[i]].merge(dp[idx[p[i]]]);
idx[p[i]] = idx[i];
}
else dp[idx[p[i]]].merge(dp[idx[i]]);
}
cout << ans;
}
