#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll dfs(ll node,vector<vector<ll>>&adj,ll money,ll p,map<ll,ll> &cost){
ll cr = money;
cr += cost[node];
for(auto el:adj[node]){
if(el!=p){
cr = max(cr,dfs(el,adj,cr,node,cost));
}
}
return cr;
}
void solve(){
ll n,s;
cin>>n>>s;
vector<vector<ll>> adj(n+10);
map<ll,ll> cost;
vector<ll> edges(n+10);
queue<ll> q;
for(ll i=0;i<n;i++){
ll x,p;
cin>>x>>p;
cost[i] = x;
if(p==0){
q.push(p);
}else{
edges[i]++;
adj[p-1].push_back(i);
}
}
ll ans = s;
while(!q.empty()){
ll node = q.front();
//cout<<node<<endl;
q.pop();
ans = max(ans,dfs(node,adj,ans,-1,cost));
}
ans = ans - s;
cout<<ans<<endl;
}
int main()
{
// freopen("input.txt","r",stdin);
// freopen("output.txt","w",stdout);
solve();
return 0;
}
