// ~~ icebear love attttt ~~
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> ii;
typedef pair<int, ii> iii;
template<class T>
bool minimize(T &a, const T &b) {
if (a > b) return a = b, true;
return false;
}
template<class T>
bool maximize(T &a, const T &b) {
if (a < b) return a = b, true;
return false;
}
#define FOR(i,a,b) for(int i=(a); i<=(b); ++i)
#define FORR(i,a,b) for(int i=(a); i>=(b); --i)
#define REP(i, n) for(int i=0; i<(n); ++i)
#define RED(i, n) for(int i=(n)-1; i>=0; --i)
#define MASK(i) (1LL << (i))
#define BIT(S, i) (((S) >> (i)) & 1)
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define all(x) x.begin(), x.end()
#define task "icebearat"
const int MOD = 1e9 + 7;
const int inf = 1e9 + 27092008;
const ll INF = 1e18 + 27092008;
const int MAX = 2e5 + 5;
int L[MAX], R[MAX];
vector<int> G[MAX];
int range[MAX], dp[MAX];
void dfs(int u, int par) {
for(int v : G[u]) if (v != par) {
dfs(v, u);
minimize(L[u], L[v]);
maximize(R[u], R[v]);
}
}
int solve(int N, int M, vector<int> F, vector<vector<int>> S) {
REP(i, N) if (i > 0) {
G[i + 1].pb(F[i] + 1);
G[F[i] + 1].pb(i + 1);
}
FOR(i, 1, N) L[i] = range[i] = inf, R[i] = -inf;
REP(i, M) REP(j, N - 1) {
minimize(L[S[i][j] + 1], j + 1);
maximize(R[S[i][j] + 1], j + 1);
}
dfs(1, -1);
FOR(i, 2, N) minimize(range[R[i]], L[i]);
FOR(i, 1, N - 1) {
dp[i] = dp[i - 1];
if (range[i] != inf)
maximize(dp[i], dp[range[i] - 1] + 1);
}
return dp[N - 1];
}
