#include <bits/stdc++.h>
#define F first
#define S second
#define pb push_back
#define ppb pop_back
#define ep insert
#define endl '\n'
#define elif else if
#define pow pwr
#define sqrt sqrtt
#define int long long
#define ll long long
#define y1 YONE
typedef unsigned long long ull;
using namespace std;
const int N=1e5+5,S=300;
int a[N],dp[N],ans[N][S],n,q,m;
vector<int> adj[2][N];
bool vis[N],b[N];
int rec(int x){
if (vis[x]) return dp[x];
vis[x]=1;
for (auto u:adj[0][x]) dp[x]=max(dp[x],rec(u)+1);
return dp[x];
}
int32_t main(){
ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
cin>>n>>m>>q;
for (int i=1;i<=m;i++){
int x,y;
cin>>x>>y;
adj[0][x].pb(y);
adj[1][y].pb(x);
}
int t,y;
cin>>t>>y;
for (int i=1;i<=n;i++) dp[i]=INT_MIN;
dp[t]=0;
for (int i=1;i<=n;i++) rec(i);
//for (int i=1;i<=n;i++) cout<<dp[i]<<' ';cout<<endl;
for (int i=1;i<=y;i++){
int x;cin>>x;
b[x]=1;
}
int ans=-1;
for (int i=1;i<=n;i++) if (!b[i]) ans=max(ans,dp[i]);
cout<<ans<<endl;
return 0;
}
