#include <iostream>
#include <vector>
using namespace std;
const int mx = 100'000;
vector<int> edge[1+mx];
vector<int> rev_edge[1+mx];
int N, M, Q;
int dest;
vector<int> excluded(1+mx, 0);
int main()
{
cin >> N >> M >> Q;
for(int j = 1; j <= M; j++)
{
int s, e;
cin >> s >> e;
edge[s].push_back(e);
rev_edge[e].push_back(s);
}
int dest, Y;
cin >> dest >> Y;
for(int y = 1; y <= Y; y++)
{
int C;
cin >> C;
excluded[C] = 1;
}
vector<int> maxdist(1+N, -1);
for(int i = 1; i <= N; i++)
{
if(!excluded[i]) maxdist[i] = max(maxdist[i], 0);
for(int j: edge[i])
maxdist[j] = max(maxdist[j], maxdist[i] + 1);
}
cout << maxdist[dest] << '\n';
}
