#define LOCAL
#define _USE_MATH_DEFINES
#include <array>
#include <cassert>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <iomanip>
#include <string>
#include <sstream>
#include <vector>
#include <queue>
#include <stack>
#include <list>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <algorithm>
#include <complex>
#include <cmath>
#include <numeric>
#include <bitset>
#include <functional>
#include <random>
#include <ctime>
using namespace std;
template <typename A, typename B>
ostream& operator <<(ostream& out, const pair<A, B>& a) {
out << "(" << a.first << "," << a.second << ")";
return out;
}
template <typename T, size_t N>
ostream& operator <<(ostream& out, const array<T, N>& a) {
out << "["; bool first = true;
for (auto& v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "]";
return out;
}
template <typename T>
ostream& operator <<(ostream& out, const vector<T>& a) {
out << "["; bool first = true;
for (auto v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "]";
return out;
}
template <typename T, class Cmp>
ostream& operator <<(ostream& out, const set<T, Cmp>& a) {
out << "{"; bool first = true;
for (auto& v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "}";
return out;
}
template <typename T, class Cmp>
ostream& operator <<(ostream& out, const multiset<T, Cmp>& a) {
out << "{"; bool first = true;
for (auto& v : a) { out << (first ? "" : ", "); out << v; first = 0;} out << "}";
return out;
}
template <typename U, typename T, class Cmp>
ostream& operator <<(ostream& out, const map<U, T, Cmp>& a) {
out << "{"; bool first = true;
for (auto& p : a) { out << (first ? "" : ", "); out << p.first << ":" << p.second; first = 0;} out << "}";
return out;
}
#ifdef LOCAL
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
#else
#define trace(...) 42
#endif
template <typename Arg1>
void __f(const char* name, Arg1&& arg1){
cerr << name << ": " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args){
const char* comma = strchr(names + 1, ',');
cerr.write(names, comma - names) << ": " << arg1 << " |";
__f(comma + 1, args...);
}
template <class T> auto vect(const T& v, int n) { return vector<T>(n, v); }
template <class T, class... D> auto vect(const T& v, int n, D... m) {
return vector<decltype(vect(v, m...))>(n, vect(v, m...));
}
using int64 = long long;
using int128 = __int128_t;
using ii = pair<int, int>;
#define SZ(x) (int)((x).size())
template <typename T> static constexpr T inf = numeric_limits<T>::max() / 2;
const int MOD = 1e9 + 7;
// const int MOD = 998244353;
// mt19937 mrand(random_device{}());
// int rnd(int x) { return mrand() % x; }
mt19937_64 mrand(random_device{}());
int64 rnd(int64 x) { return mrand() % x; }
template <class T> void out(const vector<T>& a) { for (int i = 0; i < SZ(a); ++i) cout << a[i] << " \n"[i + 1 == SZ(a)]; }
template <class T> bool ckmin(T& a, const T& b) { return b < a ? a = b, 1 : 0; }
template <class T> bool ckmax(T& a, const T& b) { return a < b ? a = b, 1 : 0; }
template <class T> void dedup(vector<T>& v) { sort(v.begin(), v.end()); v.erase(unique(v.begin(), v.end()), v.end()); }
void add_mod(int& x, int y) { x += y; if (x >= MOD) x -= MOD; }
void sub_mod(int& x, int y) { x += MOD - y; if (x >= MOD) x -= MOD; }
struct fast_ios {
fast_ios() {
cin.tie(nullptr);
ios::sync_with_stdio(false);
cout << fixed << setprecision(10);
};
} fast_ios_;
const int N = 3e5 + 10;
vector<ii> a[N];
template <typename T>
struct slope_trick {
T min_f;
priority_queue<T, vector<T>, less<>> L;
priority_queue<T, vector<T>, greater<>> R;
T add_l, add_r;
void pushR(const T& x) {
R.push(x - add_r);
}
T topR() const {
if (R.empty()) return inf<T>;
return R.top() + add_r;
}
T popR() {
T ret = topR();
if (!R.empty()) R.pop();
return ret;
}
void pushL(const T& x) {
L.push(x - add_l);
}
T topL() const {
if (L.empty()) return -inf<T>;
return L.top() + add_l;
}
T popL() {
T ret = topL();
if (!L.empty()) L.pop();
return ret;
}
size_t size() { return L.size() + R.size(); }
slope_trick() : min_f(0), add_l(0), add_r(0) {}
// f(x) += a
void add_all(const T& a) {
min_f += a;
}
// add \_
// f(x) += max(a - x, 0)
void add_a_minus_x(const T& a) {
min_f += max(T(0), a - topR());
pushR(a);
pushL(popR());
}
// add _/
// f(x) += max(x - a, 0)
void add_x_minus_a(const T& a) {
min_f += max(T(0), topL() - a);
pushL(a);
pushR(popL());
}
// add \/
// f(x) += abs(x - a)
void add_abs(const T& a) {
add_a_minus_x(a);
add_x_minus_a(a);
}
// \/ -> \_
// f_new(x) = min f(y) (y <= x)
void clear_right() {
while (!R.empty()) R.pop();
}
// \/ -> _/
// f_new(x) = min f(y) (y >= x)
void clear_left() {
while (!L.empty()) L.pop();
}
// \/ -> \_/
// f_new(x) = min f(y) (x-b <= y <= x-a)
void expand(const T& a, const T& b) {
assert(a <= b);
add_l += a;
add_r += b;
}
// \/. -> .\/
// f_new(x) = f(x - a)
void shift(const T& a) {
expand(a, a);
}
// L, R will be emptied.
T get(const T& x) {
T ret = min_f;
while (!L.empty()) ret += max(T(0), popL() - x);
while (!R.empty()) ret += max(T(0), x - popR());
return ret;
}
void merge(slope_trick& other) {
if (other.size() > size()) {
swap(other.L, L);
swap(other.R, R);
swap(other.add_l, add_l);
swap(other.add_r, add_r);
swap(other.min_f, min_f);
}
while (!other.R.empty()) add_x_minus_a(other.popR());
while (!other.L.empty()) add_a_minus_x(other.popL());
min_f += other.min_f;
}
};
slope_trick<int64> st[N];
void dfs(int u, int parent) {
int cnt = 0;
for (auto& [v, w] : a[u]) {
if (v == parent) continue;
dfs(v, u);
++cnt;
int64 topR = st[v].topR() + w;
st[v].clear_right();
st[v].pushR(topR);
int64 topL = st[v].topL() + w;
st[v].popL();
st[v].pushL(topL);
st[u].merge(st[v]);
}
if (cnt == 0) st[u].add_abs(0);
}
int main() {
int n, m;
cin >> n >> m;
n += m;
for (int i = 1; i < n; ++i) {
int p, c;
cin >> p >> c;
--p;
a[p].push_back({i, c});
}
dfs(0, -1);
cout << st[0].min_f << '\n';
return 0;
}
