#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
template<class T> using oset =
tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#define int long long
#define ld long double
#define ar array
#define vi vector<int>
#define vii vector<vector<int>>
#define pii pair<int, int>
#define pb push_back
#define all(x) x.begin(), x.end()
#define f first
#define s second
#define endl "\n"
const int MOD = 1e9+7;
const int inf = 1e9;
const int linf = 1e18;
const int d4i[4]={-1, 0, 1, 0}, d4j[4]={0, 1, 0, -1};
const int d8i[8]={-1, -1, 0, 1, 1, 1, 0, -1}, d8j[8]={0, 1, 1, 1, 0, -1, -1, -1};
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
// -------------------------------------------------- Main Code --------------------------------------------------
const int N = 305;
vector<pii> g[N];
int dp[N][N];
void dfs(int src, int par) {
for (auto child : g[src]) {
int ch = child.f, wt = child.s;
if (ch == par) continue;
dfs(ch, src);
for (int l = 0; l < N; l++) {
int mn = inf;
for (int k = 0; k <= l; k++) {
int diff = l-k;
mn = min(mn, dp[ch][k] + abs(diff-wt));
}
dp[src][l] += mn;
dp[src][l] = min(dp[src][l], inf);
}
}
if (g[src].size() == 1 && src != 1) {
// dp[src][0] = 0;
for (int i = 1; i < N; i++) dp[src][i] = inf;
}
}
void sol() {
// memset(dp, 63, sizeof dp);
int n, m; cin >> n >> m;
vi lengths;
for (int i = 2; i <= n+m; i++) {
int x, length; cin >> x >> length;
g[x].pb({i, length});
g[i].pb({x, length});
lengths.pb(length);
}
if (n == 1) {
sort(lengths.begin(), lengths.end());
int ans = 0;
for (int i = 0; i < m; i++) {
ans += abs(lengths[m / 2] - lengths[i]);
}
cout << ans;
return;
}
dfs(1, -1);
int ans = inf;
for (int i = 0; i < N; i++) ans = min(ans, dp[1][i]);
cout << ans << endl;
}
signed main () {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int t = 1;
// cin >> t;
while (t--) {
sol();
}
return 0;
}
