#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define int ll
#define len(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define pb push_back
const int MOD = 1e9 + 7;
int mod(int x) {
x %= MOD;
if (x < 0)
x += MOD;
return x;
}
const int MAXN = 310;
const int MAXA = 310;
const int INF = 1e18;
vector<vector<int>> g;
vector<vector<int>> dp;
vector<int> p;
vector<int> c;
void dfs(int u) {
dp[u].resize(MAXA, INF);
vector<int> sums(MAXA);
for (auto v : g[u]) {
dfs(v);
for (int i = 0; i < MAXA; ++i) {
sums[i] += dp[v][i];
}
}
if (!len(g[u])) {
for (int i = 0; i < MAXA; ++i) {
dp[u][i] = abs(i - c[u]);
}
return;
}
for (int x = 0; x < MAXA; ++x) {
for (int y = 0; y <= x; ++y) {
if (u == 0 && x != y)
continue;
int new_c = x - y;
dp[u][x] = min(dp[u][x], abs(c[u] - new_c) + sums[y]);
}
}
}
void run() {
int n, m;
cin >> n >> m;
g.resize(n + m);
dp.resize(n + m);
vector<int> v;
p.resize(n + m);
c.resize(n + m);
p[0] = -1;
for (int i = 1; i < n + m; ++i) {
cin >> p[i] >> c[i];
--p[i];
g[p[i]].pb(i);
v.pb(c[i]);
}
if (n == 1) {
sort(all(v));
int X = v[len(v) / 2];
int ans = 0;
for (int i = 0; i < len(v); ++i) {
ans += abs(v[i] - X);
}
cout << ans << '\n';
return;
} else {
dfs(0);
int ans = INF;
for (auto val : dp[0])
ans = min(ans, val);
cout << ans << '\n';
return;
}
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
run();
}
