/**
* @title Template
*/
#include <iostream>
#include <algorithm>
#include <utility>
#include <numeric>
#include <vector>
#include <array>
#include <cassert>
#include <iomanip>
template <class T, class U>
bool chmin(T &lhs, const U &rhs) {
if (lhs > rhs) {
lhs = rhs;
return true;
}
return false;
}
template <class T, class U>
bool chmax(T &lhs, const U &rhs) {
if (lhs < rhs) {
lhs = rhs;
return true;
}
return false;
}
/**
* @title Chmin/Chmax
*/
class range {
public:
class iterator {
private:
int64_t M_position;
public:
iterator(int64_t position) noexcept: M_position(position) { }
void operator ++ () noexcept { ++M_position; }
bool operator != (iterator other) const noexcept { return M_position != other.M_position; }
int64_t operator * () const noexcept { return M_position; }
};
class reverse_iterator {
private:
int64_t M_position;
public:
reverse_iterator(int64_t position) noexcept: M_position(position) { }
void operator ++ () noexcept { --M_position; }
bool operator != (reverse_iterator other) const noexcept { return M_position != other.M_position; }
int64_t operator * () const noexcept { return M_position; }
};
private:
const iterator M_first, M_last;
public:
range(int64_t first, int64_t last) noexcept: M_first(first), M_last(std::max(first, last)) { }
iterator begin() const noexcept { return M_first; }
iterator end() const noexcept { return M_last; }
reverse_iterator rbegin() const noexcept { return reverse_iterator(*M_last - 1); }
reverse_iterator rend() const noexcept { return reverse_iterator(*M_first - 1); }
};
/**
* @title Range
*/
#include <type_traits>
#include <iterator>
template <class T>
class rev_impl {
public:
using iterator = decltype(std::declval<T>().rbegin());
private:
const iterator M_begin;
const iterator M_end;
public:
rev_impl(T &&cont) noexcept: M_begin(cont.rbegin()), M_end(cont.rend()) { }
iterator begin() const noexcept { return M_begin; }
iterator end() const noexcept { return M_end; }
};
template <class T>
rev_impl<T> rev(T &&cont) {
return rev_impl<T>(std::forward<T>(cont));
}
/**
* @title Reverser
*/
using i32 = int32_t;
using i64 = int64_t;
using u32 = uint32_t;
using u64 = uint64_t;
constexpr i32 inf32 = (i32(1) << 30) - 1;
constexpr i64 inf64 = (i64(1) << 62) - 1;
i32 N, M, V;
std::array<i32, 300000> P, C;
struct edge_t {
const i32 to;
const i32 cost;
edge_t(i32 to_, i32 cost_): to(to_), cost(cost_) { }
};
std::array<std::vector<edge_t>, 300000> graph;
std::array<std::array<i64, 301>, 300> dp;
void dfs(i32 u) {
if (u >= N) {
dp[u].fill(inf64);
dp[u][0] = 0;
return;
}
for (auto p: graph[u]) {
const i32 v = p.to;
if (v != P[u]) {
dfs(v);
std::array<i64, 301> next;
next.fill(inf64);
for (auto j: range(0, 301)) {
for (auto k: range(0, 301 - j)) {
chmin(next[j + k], dp[v][j] + std::abs(p.cost - k));
}
}
for (auto j: range(0, 301)) {
dp[u][j] += next[j];
}
}
}
}
int main() {
std::cin >> N >> M;
V = N + M;
--P[0];
for (auto i: range(1, V)) {
std::cin >> P[i] >> C[i];
--P[i];
graph[P[i]].emplace_back(i, C[i]);
graph[i].emplace_back(P[i], C[i]);
}
if (N == 1) {
std::sort(C.begin(), C.end());
i32 goal = C[C.size() / 2];
i64 ans = 0;
for (auto x: C) {
ans += std::abs(goal - x);
}
std::cout << ans << '\n';
}
else if (V <= 300) {
dfs(0);
i64 ans = inf64;
for (auto j: range(0, 301)) {
chmin(ans, dp[0][j]);
}
std::cout << ans << '\n';
}
return 0;
}
