#include<bits/stdc++.h>
using namespace std;
#define int long long
/*
- the graph will be 'c' connected components with each cc is a tree
- we can process each cc individually
- greedy : only take a negative node if it's child can make sum that cover loss
from the current node.
*/
const int mxn = 3e5+20;
int n, s, x[mxn], dp[mxn];
vector<int> adj[mxn];
void dfs(int cur) {
int sigma = 0;
for (int nxt : adj[cur]) {
dfs(nxt);
sigma += dp[nxt];
}
dp[cur] = max(0ll, sigma + x[cur]);
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
cin >> n >> s;
for (int i = 1; i <= n; i++) {
cin >> x[i];
int p;
cin >> p;
adj[p].push_back(i);
}
dfs(0);
cout << dp[0] << '\n';
}
