#include <bits/stdc++.h>
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
//#define int long long
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int mod = 1e9 + 7;
const int LOG = 20;
const int maxn = 3e5 + 5;
const double eps = 1e-9;
int n;
ll val[maxn], S;
vector<int> graph[maxn];
ll dfs(int u) {
ll sum = val[u];
for(int &v : graph[u]) sum += dfs(v);
return max(0ll, sum);
}
int32_t main() {
ios_base::sync_with_stdio(false);
cout.tie(0); cin.tie(0);
cin >> n >> S;
for(int i=1; i<=n; i++) {
cin >> val[i];
int p;
cin >> p;
graph[p].push_back(i);
}
cout << dfs(0) << '\n';
return 0;
}
