CF - Ostap & Tree

Solution described by editorial is terrible, but we can do better! This runs in $\mathcal{O}(NK)$ time. (proof?)

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#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ld = long double;
using db = double;
using str = string;  // yay python!

using pi = pair<int, int>;
using pl = pair<ll, ll>;