//#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define srt(x) sort(all(x))
#define sz(x) (ll)(x.size())
#define pii pair < int, int >
#define pll pair < ll, ll >
#define debug(x) cerr << (#x) << " = " << (x) << endl
const int mod = 1e9 + 7;
const int N = 305;
const ll OO = 1e18;
template<typename T>
bool umn (T &fi, T se) { return fi > se ? (fi = se, 1) : 0; }
template<typename T>
bool umx (T &fi, T se) { return fi < se ? (fi = se, 1) : 0; }
int n, m, add[N];
ll w[N];
vector < int > a[N];
vector < pii > g[N];
ll calc (int i, int v) {
ll res = OO;
for (int j : a[v])
res = min(res, (ll)abs(j - i));
return res;
}
void dfs (int v) {
for (auto [u, wi] : g[v]) {
w[u] = w[v] + wi;
dfs(u);
add[v] += add[u];
}
if (v >= n) {
a[v].pb(w[v]);
} else {
ll mn = OO;
for (int i = w[v]; i <= 305; ++i) {
ll res = 0;
for (auto [u, wi] : g[v])
res += calc(i, u);
umn(mn, res);
}
for (int i = w[v]; i <= 305; ++i) {
ll res = 0;
for (auto [u, wi] : g[v])
res += calc(i, u);
if (res == mn)
a[v].pb(i);
}
add[v] += mn;
}
}
void slv () {
cin >> n >> m;
for (int i = 1, p, c; i < n + m; ++i) {
cin >> p >> c;
g[p - 1].pb({i, c});
}
dfs(0);
cout << add[0];
}
signed main () {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int test = 1;
// cin >> test;
while (test--) {
slv();
cout << "\n";
}
}
