#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;
typedef pair<int, ii> iii;
typedef pair<ii, int> ri3;
#define mp make_pair
#define pb push_back
#define fi first
#define sc second
#define SZ(x) (int)(x).size()
#define ALL(x) begin(x), end(x)
#define REP(i, n) for (int i = 0; i < n; ++i)
#define FOR(i, a, b) for (int i = a; i <= b; ++i)
#define RFOR(i, a, b) for (int i = a; i >= b; --i)
const int N = 3e5+5;
int n, m;
vector<ii> al[N];
struct Slope {
priority_queue<ll> points;
ll a = 0, b = 0;
void clean() {
while (a > 1) {
--a;
b += points.top();
points.pop();
}
}
};
void print(priority_queue<ll> pq) { while (!pq.empty()) cout << pq.top() << ' ', pq.pop(); cout << '\n'; }
Slope dfs(int u, int p)
{
Slope cur;
if (SZ(al[u]) == 1 and al[u][0].fi == p)
cur.points.push(0), cur.points.push(0), cur.a = 1, cur.b = 0;
else for (auto v : al[u]) if (v.fi != p) {
Slope nxt = dfs(v.fi, u);
ll x = nxt.points.top(); nxt.points.pop();
ll y = nxt.points.top(); nxt.points.pop();
nxt.points.push(x+v.sc);
nxt.points.push(y+v.sc);
nxt.b -= v.sc;
//cout << "POINT " << x+v.sc << " " << nxt.a << " " << nxt.b << endl;
if (SZ(nxt.points) > SZ(cur.points)) swap(nxt, cur);
while (!nxt.points.empty()) {
cur.points.push(nxt.points.top());
nxt.points.pop();
}
cur.a += nxt.a; cur.b += nxt.b;
}
//cout << u << " :: " << cur.a << " " << cur.b << "\t\t\tSZ " << cur.points.size() << endl;
cur.clean();
return cur;
}
int main()
{
//freopen("in.txt", "r", stdin);
ios::sync_with_stdio(false);
cin.tie(0);
cin >> n >> m;
FOR(i, 2, n+m){
int p, c; cin >> p >> c;
al[i].emplace_back(p, c);
al[p].emplace_back(i, c);
}
Slope ans = dfs(1, 0);
//print(ans.points); cout << ans.points.top() << " " << ans.a << " " << ans.b << endl;
cout << (ll)ans.points.top()*ans.a + ans.b << '\n';
}
