#include<bits/stdc++.h>
using namespace std;
#define rall(s) s.rbegin(), s.rend()
#define all(s) s.begin(), s.end()
#define sz(s) (int)s.size()
#define s second
#define f first
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int N = 1e6;
const ll inf = 1e18;
vector<int> g[N];
ll dp[N], x[N], p[N];
void dfs(int u) {
dp[u] = x[u];
for (int to: g[u]) {
dfs(to);
dp[u] += dp[to];
}
dp[u] = max(dp[u], 0ll);
}
void solve() {
int n, ok = 1;
ll s;
cin >> n >> s;
for (int i = 1; i <= n; i++) {
cin >> x[i] >> p[i];
if (p[i] && p[i] != i - 1) ok = 0;
}
if (ok) {
vector<int> h;
ll ans = 0, z = s;
p[n + 1] = 0;
for (int i = 1; i <= n + 1; i++) {
if (p[i]) h.push_back(i);
else {
if (sz(h)) {
ll pr[sz(h)], mn = 0;
for (int j = 0; j < sz(h); j++) {
if (j) pr[j] = pr[j - 1];
else pr[j] = 0;
pr[j] += x[h[j]];
mn = min(mn, pr[j]);
}
s += max(0ll, pr[sz(h) - 1]);
ans += pr[sz(h) - 1] - mn;
}
h = {i};
}
}
cout << max(ans, s) - z;
return;
}
for (int i = 1; i <= n; i++) {
g[p[i]].push_back(i);
}
dfs(0);
cout << dp[0];
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
solve();
}
