#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5+10;
int ans[maxn];
bool chegay[maxn];
vector<int> grafo[maxn];
int main(){
ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
int n, m, q;
cin >> n >> m >> q;
for(int i=1; i<=m; i++){
int u, v;
cin >> u >> v;
grafo[u].push_back(v);
}
int t, y;
cin >> t >> y;
vector<bool> mark(n+1, 1);
for(int i=0; i<y; i++){
int x;
cin >> x;
mark[x] = 0;
}
memset(ans, -1, sizeof ans);
ans[t] = 0;
chegay[t] = 1;
for(int u=t-1; u>=1; u--){
for(int v : grafo[u]){
if(v > t) continue;
chegay[u] |= chegay[v];
if(chegay[v]) ans[u] = max(ans[u], ans[v]);
}
if(chegay[u]) ++ans[u];
}
int tfg = -1;
for(int i=1; i<=n; i++){
if(mark[i]) tfg = max(tfg, ans[i]);
}
cout << tfg << "\n";
return 0;
}
