#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair <int, int>
#define fi first
#define se second
#define mp make_pair
#define isz(a) (int)(a).size()
const int NM = 3e5;
int N, M;
vector <pii> adj[NM+5];
pii dfs(int u, int p){
vector <int> arr = {};
int res = 0;
for (pii _ : adj[u]){
int v = _.fi, c = _.se;
if (v == p) continue;
pii tmp = dfs(v, u);
res += tmp.fi;
arr.push_back(tmp.se+c);
}
if (arr.empty()) return mp(0, 0);
sort(arr.begin(), arr.end());
int t = (isz(arr)-1)/2;
for (int x : arr) res += abs(x-arr[t]);
return mp(res, arr[t]);
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> N >> M;
for (int i = 2; i <= N+M; i++){
int p, c; cin >> p >> c;
adj[i].push_back(mp(p, c));
adj[p].push_back(mp(i, c));
}
cout << dfs(1, -1).fi;
return 0;
}
