#include <bits/stdc++.h>
#define int long long
using namespace std;
typedef array<int, 2> pr;
typedef priority_queue<pr, vector<pr>, greater<pr>> pr_pq;
const int MAX = 400000;
vector<int> adj[MAX];
int X[MAX];
pr_pq dfs(int node) {
pr_pq pq, tmp;
pr K, R;
for (int i : adj[node]) {
tmp = dfs(i);
if (tmp.size() > pq.size())
swap(tmp, pq);
while (!tmp.empty())
K = tmp.top(), tmp.pop(), pq.push(K);
}
if (X[node] >= 0)
R = {0, X[node]};
else {
R = {-X[node], X[node]};
while (!pq.empty() && R[1] <= 0)
K = pq.top(), pq.pop(), R[0] = max(R[0], K[0] - R[1]), R[1] += K[1];
}
while (!pq.empty() && pq.top()[0] <= R[0] + R[1])
K = pq.top(), pq.pop(), R[1] += K[1];
if (R[1] > 0)
pq.push(R);
return pq;
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(0), cout.tie(0);
int N, S, P, ans = 0;
pr K;
cin >> N >> S;
for (int i = 1; i <= N; i++) {
cin >> X[i] >> P;
adj[P].push_back(i);
}
X[0] = S;
pr_pq res = dfs(0);
ans = res.top()[1];
cout << ans - S << '\n';
return 0;
}
