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E.cpp
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E.cpp
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#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define pb push_back
#define mp make_pair
#define lb lower_bound
#define ub upper_bound
#define ff first
#define ss second
#define rep(i, a, b) for(int i = a; i < b; i++)
#define repR(i, a, b) for(int i = a; i >= b; --i)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) (int)(x).size()
#define mem1(a) memset(a,-1,sizeof(a))
#define mem0(a) memset(a,0,sizeof(a))
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define MOD1 1000000007
#define MOD2 998244353
#define INF 2000000000000000000
#define ps(x,y) fixed << setprecision(y) << x
#define fastio ios_base::sync_with_stdio(false),cin.tie(NULL),cout.tie(NULL)
template <typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
//member functions :
//1. order_of_key(k) : number of elements strictly lesser than k
//2. find_by_order(k) : k-th element in the set
int n, q, timer;
vector<vector<int>> adj;
vector<int> lv, sub, order;
int dfs(int u, int p)
{
order.pb(u);
sub[u] = 1;
lv[u] = timer++;
for (auto v : adj[u]) {
if (v != p) {
sub[u] += dfs(v, u);
}
}
return sub[u];
}
void solve()
{
cin >> n >> q;
adj = vector<vector<int>> (n);
lv = vector<int> (n, 0);
sub = vector<int> (n, 0);
rep(u, 1, n) {
int v; cin >> v;
--v;
adj[u].pb(v);
adj[v].pb(u);
}
rep(i, 0, n) {
sort(all(adj[i]));
}
dfs(0, -1);
while (q--) {
int u, k;
cin >> u >> k;
--u;
if (sub[u] < k) cout << -1 << '\n';
else cout << order[lv[u] + k - 1] + 1 << '\n';
}
}
int main()
{
fastio;
/*#ifndef ONLINE_JUDGE
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif*/
int t = 1;
//cin >> t;
while (t--) solve();
return 0;
}