//CAUTION : this template is only suitable with C++17 (above) and home training, do not abuse when practicing offline
#include <bits/stdc++.h>
using namespace std;
//Benq inspires me lol
#define tcT template<class T
#define tcTU tcT, class U
//pairs
#define mp make_pair
#define mt make_tuple
#define ff first
#define ss second
//vectors
#define sz(v) (int)v.size()
#define all(v) begin(v), end(v)
#define rall(v) rbegin(v), rend(v)
#define pb push_back
#define eb emplace_back
#define compact(v) v.erase(unique(all(v)), end(v))
tcT> int lwb(const vector<T>& a, const T& b){ return int(lower_bound(all(a), b) - begin(a)); }
tcT> int upb(const vector<T>& a, const T& b){ return int(upper_bound(all(a), b) - begin(a)); }
//loops (warning : ONLY for int)
#define rep(i, l, r) for(int i = (l); i < (r); ++i)
#define FOR(i, l, r) for(int i = (l); i <= (r); ++i)
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#endif //LOCAL
//data types
using ll = long long;
using db = double;
using ld = long double;
using pi = pair<int, int>;
using pl = pair<ll, ll>;
using vi = vector<int>;
using vl = vector<ll>;
using vb = vector<bool>;
using vd = vector<db>;
using vc = vector<char>;
using vstr = vector<string>;
using vpi = vector<pi>;
using vpl = vector<pl>;
tcT> using min_heap = priority_queue<T, vector<T>, greater<T>>;
tcT> using max_heap = priority_queue<T>;
//bitwise operations
#define popcount(x) __builtin_popcountll(x) //count bits
#define BIT(k) (1LL << k) //bit k-th
//functions
tcT> bool minimize(T& a, const T& b){ if(a > b) return a = b, true; return false; }
tcT> bool maximize(T& a, const T& b){ if(a < b) return a = b, true; return false; }
tcT> T ceil_div(T a, T b){ return (a / b) + ((a ^ b) > 0 && a % b); }
tcT> T floor_div(T a, T b){ return (a / b) - ((a ^ b) < 0 && a % b); }
tcT> void safe_erase(vector<T>& a, T x){
auto it = find(all(a), x);
if(it != a.end()) a.erase(it);
}
#ifdef LOCAL //for checking time elapsed
const auto start_time = std::chrono::high_resolution_clock::now();
db time_elapsed(){ return chrono::duration<db>(std::chrono::high_resolution_clock::now() -
start_time).count(); }
#endif //LOCAL
void setIO(){
ios_base::sync_with_stdio(0); cin.tie(0);
#define task "task"
if(fopen(task".inp", "r")){
freopen(task".inp", "r", stdin);
// freopen(task".out", "w", stdout);
}
}
const int MAX = 3e5 + 5;
int N, M;
vpi adj[MAX];
ll min_f[MAX];
pl optimum[MAX];
void dfs(int u, int p){
max_heap<ll> L; min_heap<ll> R;
for(auto [v, w] : adj[u]) if(v != p){
if(N + 1 <= v){
//leaf
optimum[v] = {0, 0};
min_f[v] = 0;
} else{
dfs(v, u);
}
min_f[u] += min_f[v];
L.push(optimum[v].ff + w);
R.push(optimum[v].ss + w);
}
assert(!L.empty() && !R.empty());
while(L.top() > R.top()){
ll l = L.top(); L.pop();;
ll r = R.top(); R.pop();
min_f[u] += l - r;
L.push(r);
R.push(l);
}
optimum[u] = {L.top(), R.top()};
}
void testcase(int n_case){
cin >> N >> M;
for(int i = 2; i <= N + M; ++i){
int p, w;
cin >> p >> w;
adj[p].eb(i, w);
}
dfs(1, -1);
cout << min_f[1] << '\n';
}
int main(){
setIO();
int T = 1;
// cin >> T;
rep(i, 0, T) testcase(i);
#ifdef LOCAL
cerr << '\n' << "Execution time : " << (time_elapsed() * 1000.0) << " ms";
#endif //LOCAL
return 0;
}
