#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MAX = 300010;
int n, m;
int p[2 * MAX];
ll c[2 * MAX];
vector<pair<int, ll>> g[MAX];
struct state
{
ll cost, distance, wiggle_room;
};
pair<ll,ll> dp(int u)
{
if (u > n)
return {0, 0};
ll res = 0;
vector<ll> times;
ll min_val = 0;
for (auto [v, l] : g[u])
{
auto [t, d] = dp(v);
res += t;
times.push_back(l + d);
min_val = max(min_val, d);
}
vector<ll> t = times;
sort(t.begin(), t.end());
if (min_val >= t[t.size() / 2])
{
ll best = min_val;
for (ll x : times)
res += abs(best - x);
return {res, best};
}
ll best = t[(t.size() - 1) / 2];
for (ll x : times)
res += abs(best - x);
return {res, best};
}
int main()
{
cin.tie(0)->sync_with_stdio(0);
cin >> n >> m;
p[1] = -1, c[1] = 0;
for (int i = 2; i <= n + m; i++)
{
cin >> p[i] >> c[i];
g[p[i]].push_back({i, c[i]});
}
cout << dp(1).first << '\n';
return 0;
}
