/*
* author : Apiram
* created: 11.08.2024 14:11:10
*/
#include<bits/stdc++.h>
using namespace std;
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
long long n,s;cin>>n>>s;
vector<pair<long long,long long>>arr(n + 1);
vector<vector<long long>>adj(n + 1);
for (long long i = 1;i<=n;++i){
cin>>arr[i].first>>arr[i].second;
adj[arr[i].second].push_back(i);
}
long long k = s;
priority_queue<pair<long long,long long>>q;
for (auto x:adj[0]){
q.push({arr[x].first,x});
}
while(!q.empty()){
auto u = q.top();
q.pop();
if (u.first > 0){
k+=u.first;
for (auto x:adj[u.second]){
q.push({arr[x].first,x});
}
}
else if (k + u.first >= 0){
for (auto x:adj[u.second]){
q.push({arr[x].first + u.first,x});
}
}
else break;
}
cout<<k - s<<'\n';
return 0;
}
