#include <bits/stdc++.h>
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define endl "\n"
#define all(x) (x).begin(), (x).end()
using ll = long long;
using namespace std;
int solve(int N, int M, vector<int> F, vector<vector<int>> S) {
vector<vector<int>> tree(N);
vector<int> indegree(N, 0);
for (int i = 1; i < N; i++) {
tree[F[i]].push_back(i);
indegree[i]++;
}
queue<int> q;
for (int i = 1; i < N; i++) {
if (indegree[i] == 0) q.push(i);
}
unordered_map<int, int> volunteer_pos[M];
for (int i = 0; i < M; i++) {
for (int j = 0; j < N - 1; j++) {
volunteer_pos[i][S[i][j]] = j;
}
}
auto is_valid = [&](int days) {
vector<int> order(N - 1, -1);
queue<int> temp_q = q;
int day = 0;
while (!temp_q.empty() && day < days) {
int size = temp_q.size();
vector<int> today;
while (size--) {
int node = temp_q.front();
temp_q.pop();
today.push_back(node);
}
sort(all(today), [&](int a, int b) {
int min_pos_a = N, min_pos_b = N;
for (int i = 0; i < M; i++) {
min_pos_a = min(min_pos_a, volunteer_pos[i][a]);
min_pos_b = min(min_pos_b, volunteer_pos[i][b]);
}
return min_pos_a < min_pos_b;
});
for (int x : today) order[x] = day;
for (int x : today) {
int parent = F[x];
indegree[parent]--;
if (indegree[parent] == 0 && parent != 0) temp_q.push(parent);
}
day++;
}
for (int i = 0; i < M; i++) {
for (int j = 1; j < N - 1; j++) {
if (order[S[i][j]] < order[S[i][j - 1]]) return false;
}
}
return true;
};
int lo = 1, hi = N - 1, ans = 1;
while (lo <= hi) {
int mid = (lo + hi) / 2;
if (is_valid(mid)) {
ans = mid;
lo = mid + 1;
} else {
hi = mid - 1;
}
}
return ans;
}
