#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'; }