#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((lint)(x).size())
#define POW2(n) (1LL << (n))
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const deque<T> &vec){ os << "deq["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &pa){ os << "(" << pa.first << "," << pa.second << ")"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const unordered_map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }
template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }
template<typename T> bool mmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template<typename T> bool mmin(T &m, const T q) { if (m > q) {m = q; return true;} else return false; }
template<typename T1, typename T2> pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template<typename T1, typename T2> pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/tag_and_trait.hpp>
using namespace __gnu_pbds; // find_by_order(), order_by_key()
template<typename TK> using pbds_set = tree<TK, null_type, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename TK, typename TV> using pbds_map = tree<TK, TV, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;
*/

struct UndirectedGraph
{
    using Pint = pair<int, int>;
    using Plint = pair<lint, int>;
    int V;
    int E;
    int dDefault;
    vector<lint> weights;
    vector<vector<Pint>> to;
    vector<Pint> edges;

    UndirectedGraph(int V, lint dDefault=-1) : V(V), E(0), dDefault(dDefault),
                             to(vector<vector<Pint>>(V)) {}

    void add_edge(int v1, int v2, lint w)
    {
        to[v1].push_back(Pint(v2, E));
        // to[v2].push_back(Pint(v1, E));
        edges.push_back(Pint(v1, v2));
        weights.push_back(w);
        E++;
    }

    vector<lint> dist;
    void dijkstra(int start)
    {
        dist = vector<lint>(V, dDefault);
        priority_queue<Plint, vector<Plint>, greater<Plint>> pq;
        pq.push(Plint(0, start));

        while (!pq.empty()) {
            Plint p = pq.top(); pq.pop();
            int v = p.second;
            if (dist[v] >= 0 && dist[v] <= p.first) continue;
            dist[v] = p.first;
            // cout << "dist[" << v << "] = " << p.first << endl;
            for (auto vnxt : to[v]) {
                lint dnxt = dist[v] + weights[vnxt.second];
                if (dnxt < dist[vnxt.first] || dist[vnxt.first] < 0) {
                    pq.push(Plint(dnxt, vnxt.first));
                }
            }
        }
    }
};
int main()
{
    lint N;
    cin >> N;
    lint M;
    cin >> M;
    vector<lint> u(M);
    vector<lint> v(M);
    REP(i, M){ cin >> u[i]; cin >> v[i]; }
    lint S;
    cin >> S;
    lint T;
    cin >> T;
    UndirectedGraph graph(N * 3 + 10);

    REP(i, M)
    {
        graph.add_edge(u[i] * 3, v[i] * 3 + 1, 1);
        graph.add_edge(u[i] * 3 + 1, v[i] * 3 + 2, 1);
        graph.add_edge(u[i] * 3 + 2, v[i] * 3, 1);
    }
    graph.dijkstra(S * 3);
    int ret = graph.dist[T * 3];
    // dbg(ret);
    cout << (ret > 0 ? ret / 3 : -1) << endl;
    return 0;
}


Measured memory_bytes: 27224