#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
template< typename T >
struct SlopeTrick {
T INF = numeric_limits< T >::max() / 3;
T min_f, add_l, add_r;
priority_queue< T, vector< T >, less<> > L;
priority_queue< T, vector< T >, greater<> > R;
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);
}
// 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) {
if (a > top_R()) {
min_f+=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;push_R(pop_L());push_L(a);
} else {
push_R(a);
}
}
// add \/ ; f(x) += max(x - a, 0)
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.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; }
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 SmallToLarge(SlopeTrick<LL> &from,
SlopeTrick<LL>&to) {
if (from.L.size()+from.R.size()>
to.L.size()+to.R.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;
}
