//#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 = 1e5+1;
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;
vector < pii > g[N];
pll res[N];
ll add[N], w[N];
int calc (int i, int l, int r) {
if (!r || l <= i && i <= r)
return 0;
return min(abs(i - l), abs(i - r));
}
void dfs (int v) {
map < ll, int > mp;
for (auto [u, wi] : g[v]) {
w[u] = w[v] + wi;
dfs(u);
add[v] += add[u];
if (res[u].first) {
mp[w[v]]++;
mp[res[u].first]--;
mp[res[u].second]--;
}
}
if (v > n) {
res[v] = {w[v], w[v]};
} else {
res[v] = {10000, 0};
ll mn = OO;
for (int i = w[v]; i <= 305; ++i) {
ll ri = 0;
for (auto [u, wi] : g[v])
ri += calc(i, res[u].first, res[u].second);
umn(mn, ri);
}
for (int i = w[v]; i <= 305; ++i) {
ll ri = 0;
for (auto [u, wi] : g[v])
ri += calc(i, res[u].first, res[u].second);
if (ri == mn) {
umn(res[v].first, (ll)i);
umx(res[v].second, (ll)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";
}
}
