#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ld long double
#define pii pair<int, int>
#define fi first
#define se second
#define __builtin_popcount __builtin_popcountll
#define all(x) (x).begin(), (x).end()
#define debug(a, l, r) for (int i = (l); i <= (r); ++i) cout << (a)[i] << ' '; cout << '\n';
const int MAXN = 1e5 + 5;
const int INF = 1e18 + 7;
int n, m, q;
vector<int> radj[MAXN];
void init() {
cin >> n >> m >> q;
for (int i = 1; i <= m; ++i) {
int u, v; cin >> u >> v;
radj[v].push_back(u);
}
}
namespace subtask12{
int dp[MAXN];
bitset<MAXN> mark;
bool check() {
return (q == 1);
}
void solve() {
int t, y; cin >> t >> y;
mark.set();
for (int i = 1; i <= y; ++i) {
int c; cin >> c;
mark[c] = 0;
}
for (int i = 1; i <= n; ++i) dp[i] = -INF;
dp[t] = 0;
for (int i = t; i >= 1; --i) {
if (dp[i] == -INF) continue;
for (int j : radj[i]) {
dp[j] = max(dp[j], dp[i] + 1);
}
}
int res = -INF;
for (int i = 1; i <= n; ++i)
if (mark[i]) res = max(res, dp[i]);
cout << (res == -INF ? -1 : res);
}
}
signed main() {
#ifdef NCTHANH
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
ios_base::sync_with_stdio(0);
cin.tie(nullptr); cout.tie(nullptr);
init();
if (subtask12::check()) return subtask12::solve(), 0;
return 0;
}
