#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimize("Ofast,unroll-loops")
using namespace std;
using namespace __gnu_pbds;
#define pb push_back
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define f first
#define s second
#define int long long
#define ll long long
#define pii pair<int,int>
#define ar array
template<class T>bool umax(T &a,T b){if(a<b){a=b;return true;}return false;}
template<class T>bool umin(T &a,T b){if(b<a){a=b;return true;}return false;}
template<class T> using st = tree<T, null_type, less_equal<T>,
rb_tree_tag, tree_order_statistics_node_update>;
const int inf = 1e17 + 7;
const int mod = 1e9 + 7;
const int N = 3e5 + 5;
const int md = 998244353;
int binpow(int a, int b){
if(b == 0)return 1;
if(b % 2 == 0){
int c = binpow(a,b/2);
return (c*c)%mod;
}
return (binpow(a,b-1)*a)%mod;
}
int divi(int a, int b){
return (a*(binpow(b,mod-2)))%mod;
}
int n,m,k;
vector<int>g[N];
vector<int>dp(N);
void dfs(int x){
for(auto to:g[x]){
if(dp[to] < dp[x] + 1){
dp[to] = dp[x] + 1;
dfs(to);
}
}
}
void solve(){
cin >> n >> m >> k;
while(m--){
int a,b;
cin >> a >> b;
//~ g[a].pb(b);
g[b].pb(a);
}
int x,y;
cin >> x >> y;
vector<int>vis(n+1);
for(int i = 0;i<y;i++){
int a;
cin >> a;
vis[a] = 1;
}
dfs(x);
int mx = -1;
for(int i = 1;i<=n;i++){
if(vis[i])continue;
if(dp[i] == 0 && i != x)dp[i] = -1;
umax(mx, dp[i]);
}
cout << mx << "\n";
}
/*
*/
signed main()
{
// freopen("seq.in", "r", stdin);
// freopen("seq.out", "w", stdout);
ios_base::sync_with_stdio(0);cin.tie(NULL);cout.tie(NULL);
int tt=1;//cin>>tt;
while(tt--)solve();
}
