#include <bits/stdc++.h>
using namespace std;
#define int long long
#define INF 1e18
int n;
vector<int> p;
vector<vector<int>> adj;
vector<multiset<pair<int, int>>> dp;
void dfs(int u) {
vector<pair<int, int>> c;
for (int v : adj[u]) {
dfs(v);
while (!dp[v].empty()) {
dp[u].insert(*dp[v].begin());
dp[v].erase(dp[v].begin());
}
}
if (p[u] >= 0) {
dp[u].insert({0, p[u]});
} else {
int req = -p[u], prof = p[u];
while (!dp[u].empty() && (prof < 0 || req > dp[u].begin()->first)) {
req = max(req, dp[u].begin()->first - prof);
prof += dp[u].begin()->second;
dp[u].erase(dp[u].begin());
}
dp[u].insert({req, prof});
}
}
void solve() {
cin >> n;
adj.resize(n + 1);
p.resize(n + 1); cin >> p[0];
for (int i = 1; i <= n; i++) {
int dep; cin >> p[i] >> dep;
adj[dep].push_back(i);
}
dp.resize(n + 1);
dfs(0);
int ans = p[0];
for (auto [req, prof] : dp[0]) {
if (ans >= req && prof >= 0) {
ans += prof;
}
}
cout << ans - p[0];
}
int32_t main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
solve();
return 0;
}
