#include <bits//stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef tree<long long, null_type, less<long long>, rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;
typedef tree<long long, null_type, less_equal<long long>, rb_tree_tag,
tree_order_statistics_node_update>
ordered_multiset;
#define ll long long
#define iloop(m, h) for (auto i = m; i != h; i += (m < h ? 1 : -1))
#define jloop(m, h) for (auto j = m; j != h; j += (m < h ? 1 : -1))
#define kloop(m, h) for (auto k = m; k != h; k += (m < h ? 1 : -1))
#define pll pair<ll, ll>
#define INF 1000000000000000
#define MOD1 1000000007
#define MOD2 998244353
#define MOD3 1000000009
ll n, a[300005];
vector<ll> adj[300005];
multiset<pll> ms[300005];
void dfs(ll nd) {
for (auto it : adj[nd]) {
dfs(it);
if (ms[nd].size() < ms[it].size()) {
swap(ms[nd], ms[it]);
}
for (auto it2 : ms[it]) ms[nd].insert(it2);
}
pll cs = {max(-a[nd], 0LL), a[nd]};
while (ms[nd].size() && (cs.second < 0 || cs.second + cs.first >= (*ms[nd].begin()).first)) {
cs.first = max(cs.first, (*ms[nd].begin()).first - cs.second);
cs.second += (*ms[nd].begin()).second;
ms[nd].erase(ms[nd].begin());
}
if (cs.second >= 0) ms[nd].insert(cs);
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> a[0];
ll t1;
iloop(1, n+1) {
cin >> a[i] >> t1;
adj[t1].push_back(i);
}
dfs(0);
cout << ((ms[0].size() && (*ms[0].begin()).first == 0) ? ((*ms[0].begin()).second - a[0]) : 0);
}
