#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
/**
* @brief Slope-Trick
* @see https://maspypy.com/slope-trick-1-%E8%A7%A3%E8%AA%AC%E7%B7%A8
*/
template< typename T >
struct SlopeTrick {
T INF = numeric_limits< T >::max() / 3;
T min_f;
priority_queue< T, vector< T >, less<> > L;
priority_queue< T, vector< T >, greater<> > R;
T add_l, add_r;
//private:
void push_R(const T &a) {
R.push(a - add_r);
}
T top_R() const {
return R.top() + add_r;
}
T pop_R() {
T val = top_R();
R.pop();
return val;
}
void push_L(const T &a) {
L.push(a - add_l);
}
T top_L() const {
return L.top() + add_l;
}
T pop_L() {
T val = top_L();
L.pop();
return val;
}
public:
SlopeTrick() : min_f(0), add_l(0), add_r(0) {
L.push(-INF);
R.push(INF);
}
int size() {
return int(L.size()) + int(R.size()) - 2;
}
struct Query {
T lx, rx, min_f;
};
// return min f(x)
Query query() const {
return (Query) {top_L(), top_R(), min_f};
}
// f(x) += a
void add_all(const T &a) {
min_f += a;
}
/// has room for improvement
// add \_
// f(x) += max(a - x, 0)
void add_a_minus_x(const T &a) {
if (a > top_R()) min_f += a - top_R();
if (a > top_R()) {
push_L(pop_R());
push_R(a);
} else {
push_L(a);
}
}
// add _/
// f(x) += max(x - a, 0)
void add_x_minus_a(const T &a) {
if (top_L() > a) min_f += top_L() - a;
if (top_L() > a) {
push_R(pop_L());
push_L(a);
} else {
push_R(a);
}
}
// add \/
// f(x) += abs(x - a)
// void add_abs(const T &a) {
// add_a_minus_x(a);
// add_x_minus_a(a);
// }
void add_abs(const T &a) {
if (a < top_L()) {
min_f += top_L() - a;
push_R(pop_L());
push_L(a);
push_L(a);
} else if (top_R() < a) {
min_f += a - top_R();
push_L(pop_R());
push_R(a);
push_R(a);
} else {
push_L(a);
push_R(a);
}
}
// \/ -> \_
// f_{new} (x) = min f(y) (y <= x)
void clear_right() {
while(R.size() >= 2) R.pop();
}
// \/ -> _/
// f_{new} (x) = min f(y) (y >= x)
void clear_left() {
while(L.size() >= 2) L.pop();
}
// \/. -> .\/
// f_{new} (x) = f(x - a)
void shift(const T &a) {
add_l += a;
add_r += a;
}
///This object is no more usable after this function
T get(const T &x) {
T ret = min_f;
if (!L.empty() && x < top_L()) {
while(!L.empty()) {
ret += max(T(0), pop_L() - x);
}
}
if (!R.empty() && top_R() < x) {
while(!R.empty()) {
ret += max(T(0), x - pop_R());
}
}
return ret;
}
};
void print(SlopeTrick<LL>t) {
cout << "R:";
while (t.R.size() >= 2) cout << " " << t.pop_R();
cout << endl;
cout << "min_f " << t.min_f << endl;
cout << "L:";
while (t.L.size() >= 2) cout << " " << t.pop_L();
cout << endl;
}
void SmallToLarge(SlopeTrick<LL> &from, SlopeTrick<LL> &to) {
if (from.size() > to.size()) swap(from, to);
while (from.L.size() >= 2) {
to.add_a_minus_x(from.pop_L());
}
while (from.R.size() >= 2) {
to.add_x_minus_a(from.pop_R());
}
to.min_f += from.min_f;
}
const int MAXN = 3e5+7;
int P[MAXN], C[MAXN];
vector< int >child[MAXN];
SlopeTrick<LL> trick[MAXN];
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
int n, m;
cin >> n >> m;
for (int i = 2; i <= n+m; i++) {
cin >> P[i] >> C[i];
child[P[i]].push_back(i);
}
for (int i = n+1; i <= n+m; i++) {
trick[i].add_abs(C[i]);
}
for (int i = n; i > 0; i--) {
for (int c : child[i]) {
SmallToLarge(trick[c], trick[i]);
}
{ ///clearing all slopes greater than 1
LL save = trick[i].top_R();
trick[i].clear_right();
trick[i].push_R(save);
}
if (i > 1) {
trick[i].push_L(trick[i].pop_L()+C[i]);
trick[i].push_R(trick[i].pop_R()+C[i]);
}
}
cout << trick[1].min_f << "\n";
return 0;
}
