#include <iostream>
#include <set>
#include <vector>
#include <assert.h>
#include <map>
#include <list>
#define vi vector<int>
#define pub push_back
#define pii pair<int, int>
#define fst first
#define snd second
using namespace std;
int n, k, cnt[200001] = {}, mn = 1e9;
bool spc[200001];
list<int> adj[200001];
vi par;
void dfs(int u, int p)
{
int h = par.size();
par.push_back(u);
cnt[par[h / 2 + 1]] += spc[u];
spc[u] = 0;
for (auto v : adj[u])
{
// cout << u << " - " << v << "\n";
if (v != p) dfs(v, u);
}
par.pop_back();
}
map<int, int>* dfs2(int u, int p, int h)
{
map<int, int>* ret = new map<int, int>;
map<int, int>* rr;
(*ret)[-h]++;
for (auto v : adj[u])
{
if (v != p)
{
rr = dfs2(v, u, h + 1);
if (rr -> size() > ret -> size()) {swap(rr, ret);}
for (auto v : *rr) {(*ret)[v.fst] += v.snd;}
}
}
for (int i = 0; i < cnt[u]; i++)
{
mn = min(mn, -(ret -> begin() -> fst));
(ret -> begin() -> snd)--;
if (ret -> begin() -> snd == 0) {ret -> erase(ret -> begin());}
}
return ret;
}
int main()
{
ios :: sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> k;
for (int i = 1; i < n; i++)
{
int v; cin >> v;
adj[v - 1].push_back(i);
adj[i].push_back(v - 1);
}
for (int i = 0; i < k; i++)
{
int x; cin >> x; spc[x - 1] = 1;
}
if (spc[0]) {cout << "1\n";}
else
{
dfs(0, -1); dfs2(0 ,-1, 0);
cout << mn + 1 << '\n';
}
return 0;
}
