#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
const int maxn = 1000 + 1;
const int maxm = 2000 + 1;
vector <int> adj[maxn], adjr[maxn];
bool dp[maxn][maxm];
bool ready[maxn][maxm];
bool blocked[maxn];
int max_len = -1;
bool solve(int s, int steps) {
if (ready[s][steps])
return dp[s][steps];
bool ans = false;
for (auto i : adjr[s]) {
auto res = solve(i, steps+1);
if (res) {
ans = true;
if (!blocked[i])
max_len = max(max_len, steps+1);
}
}
if (!blocked[s]) {
ans = true;
max_len = max(max_len, steps);
}
ready[s][steps] = true;
dp[s][steps] = ans;
return ans;
}
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);
}
int t, y;
cin >> t >> y;
for (int i = 0; i < y; i++) {
int x;
cin >> x;
blocked[x] = true;
}
solve(t, 0);
cout << max_len << '\n';
}
