#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
using namespace std;
const int maxn = 1e5 + 1;
vector <int> adj[maxn], adjr[maxn];
int indeg[maxn], outdeg[maxn], processed[maxn];
bool blocked[maxn];
int main() {
int n, m, q;
cin >> n >> m >> q;
for (int i = 0; i < m; i++) {
int a, b;
cin >> a >> b;
adj[a].push_back(b);
adjr[b].push_back(a);
indeg[b]++;
outdeg[a]++;
}
int t, y;
cin >> t >> y;
for (int i = 0; i < y; i++) {
int x;
cin >> x;
blocked[x] = true;
}
int ans = -1;
priority_queue <pair <int, int>> pq;
pq.push({0, t});
vector <int> dis(n+1, -1);
dis[t] = 0;
while (!pq.empty()) {
int a = pq.top().second;
pq.pop();
if (processed[a])
continue;
processed[a] = true;
if (!blocked[a])
ans = max(ans, dis[a]);
for (auto i : adjr[a]) {
indeg[i]--;
pq.push({-indeg[i], i});
dis[i] = dis[a] + 1;
if (!blocked[i])
ans = max(ans, dis[i]);
}
}
cout << ans << '\n';
}
