#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define pii pair<ll,ll>
#define sz size()
#define all(v) v.begin(),v.end()
#define fi first
#define se second
const int N = 2e5;
const int mod = 1e9+7;
const ll INF = 1e18;
const int di[] = {1, -1, 0, 0};
const int dj[] = {0, 0, 1, -1};
void solve() {
ll n,s;
cin>>n>>s;
ll val[n+1],p[n+1];
for(int i = 1; i <= n; i++){
cin>>val[i]>>p[i];
}
set<pair<pii,ll>> st;
pair<pii,ll> nxt[n+1];
bool used[n+1];
memset(used,0,sizeof(used));
for(int i = n, id = 1; i >= 1; i--){
if(!used[i]){
vector<ll> v;
vector<pii> vec;
ll cur=i;
while(cur!=0){
v.pb(cur);
used[cur]=true;
cur=p[cur];
}
reverse(all(v));
ll x=0,s=0;
for(int j = 0; j < v.sz; j++){
x+=val[v[j]];
if(x<0)
s=min(s,x);
if(x>0){
vec.pb({abs(s),x});
x=s=0;
}
}
if(!vec.empty() && vec[0].se>0)
st.insert({vec[0],id+1});
for(int j = 0; j < vec.sz; j++){
if(j==vec.sz-1){
nxt[id]={vec[j],-1};
}
else{
nxt[id]={vec[j],id+1};
}
id++;
}
id++;
}
}
ll ans=s,x=s;
while(!st.empty()){
auto it=*st.begin();
st.erase(it);
if(x>=it.fi.fi){
x+=it.fi.se;
ans=max(ans,x);
if(it.se!=-1 && nxt[it.se].fi.se>0)
st.insert(nxt[it.se]);
}
else break;
}
cout<<ans-s<<"\n";
}
int main() {
//freopen("cowrun.in","r",stdin);
//freopen("cowrun.out","w",stdout);
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int t=1;
//cin>>t;
while(t--) {
solve();
}
return 0;
}
