#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define int ll
const int inf = 1e18;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> p2;
#define rep(i, high) for (int i = 0; i < (high); i++)
#define repp(i, lo, high) for (int i = (lo); i < (high); i++)
#define repe(i, container) for (auto& i : container)
#define sz(x) ((int)(x).size())
#define all(x) begin(x), end(x)
map<int, int> dp(int u, vvi & adj, vi & value)
{
vector<map<int, int>> children;
repe(e, adj[u])
{
map<int, int> c = dp(e, adj, value);
children.push_back(c);
}
map<int, int> ret;
int v = value[u];
priority_queue<p2> pq;
rep(i, sz(children))
{
if (sz(children[i])) pq.emplace(-begin(children[i])->first, i);
}
if (v>=0)
{
int s = 0;
int p = v;
int oldp = 0;
while (sz(pq))
{
int x = -1;
while (sz(pq))
{
auto [f, i] = pq.top();
f = -f;
if (s + p < f)
{
x = f;
break;
}
pq.pop();
p += begin(children[i])->second;
children[i].erase(begin(children[i]));
if (sz(children[i])) pq.emplace(-begin(children[i])->first, i);
}
ret[s] = p - oldp;
if (x != -1)
{
s += x - p - s;
}
p = oldp;
}
ret[s] = max(ret[s], p - oldp);
}
else
{
int s = -v;
int p = v;
int oldp = 0;
while (sz(pq))
{
int x = -1;
while (sz(pq))
{
auto [f, i] = pq.top();
f = -f;
if (s + p < f)
{
x = f;
break;
}
pq.pop();
p += begin(children[i])->second;
children[i].erase(begin(children[i]));
if (sz(children[i])) pq.emplace(-begin(children[i])->first, i);
}
ret[s] = p - oldp;
if (x != -1)
{
s += x - p - s;
}
p = oldp;
}
ret[s] = max(ret[s], p - oldp);
}
return ret;
}
signed main()
{
cin.tie(0)->sync_with_stdio(0);
int n, s;
cin >> n >> s;
vi nodevalue(n+1);
vvi adj(n+1);
rep(i, n)
{
int p, v;
cin >> v >> p;
nodevalue[i] = v;
if (p == 0) adj.back().push_back(i);
else adj[p-1].push_back(i);
}
nodevalue.back() = s;
map<int, int> res = dp(n, adj, nodevalue);
cout << begin(res)->second-s;
return 0;
}
