#include "bits/stdc++.h"
using namespace std;
#define int long long
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int n, m, q;
cin >> n >> m >> q;
vector <vector <int>> g(n + 1);
for (int i = 1; i <= m; i ++) {
int u, v;
cin >> u >> v;
g[v].push_back(u);
}
for (int i = 1; i <= n; i ++) {
sort(g[i].rbegin(), g[i].rend());
}
int begin;
cin >> begin;
int t; cin >> t;
set <int> w;
for (int i = 0; i < t; i ++) {
int x; cin >> x;
w.insert(x);
}
vector <int> dis(n + 1, - (int)1e18), vis(n + 1);
if (w.count(begin) == 0) dis[begin] = 0;
else {
cout << -1 << endl;
return 0;
}
for (int i = begin; i >= 1; i --) {
for (int x : g[i]) {
dis[x] = max(dis[x], dis[i] + 1);
}
}
int ans = -1;
for (int i = 1; i <= begin; i ++) {
if (w.count(i)) continue;
ans = max(ans, dis[i]);
}
cout << ans << endl;
return 0;
}
