#include <bits/stdc++.h>
using namespace std;

namespace {
    #define DUMPOUT cerr
    #ifndef DEBUG_
    #define dump(...)
    #else
    #define dump(...)                                                                       \
        DUMPOUT << "  ";                                                                    \
        DUMPOUT << #__VA_ARGS__ << " :[" << __LINE__ << ":" << __FUNCTION__ << "]" << endl; \
        DUMPOUT << "    ";                                                                  \
        dump_func(__VA_ARGS__)
    #endif
    void dump_func()
    {
        DUMPOUT << endl;
    }
    template <class Head, class... Tail>
    void dump_func(Head &&head, Tail &&... tail)
    {
        DUMPOUT << head;
        if (sizeof...(Tail) == 0)
        {
            DUMPOUT << " ";
        }
        else
        {
            DUMPOUT << ", ";
        }
        dump_func(std::move(tail)...);
    }
    template <class T>
    ostream &operator<<(ostream &os, const vector<T> &v)
    {
        for (auto i = begin(v); i != end(v); ++i)
            os << *i << (i == end(v) - 1 ? "" : " ");
        return os;
    }
    template <class T>
    void out2Dvector(vector<T> v)
    {
        for (const auto &vv : v)
            cout << vv << endl;
    }
    template <class T>
    istream &operator>>(istream &is, vector<T> &v)
    {
        for (auto i = begin(v); i != end(v); ++i)
            is >> *i;
        return is;
    }
    template <typename T, typename U>
    ostream &operator<<(ostream &os, pair<T, U> &pair_var)
    {
        os << "(" << pair_var.first << ", " << pair_var.second << ")";
        return os;
    }
    template <typename T, typename U>
    ostream &operator<<(ostream &os, map<T, U> &map_var)
    {
        os << "{";
        for (auto itr = map_var.begin(); itr != map_var.end(); itr++)
        {
            os << "(" << itr->first << ", " << itr->second << ")";
            itr++;
            if (itr != map_var.end())
                os << ", ";
            itr--;
        }
        os << "}";
        return os;
    }
    template <typename T>
    ostream &operator<<(ostream &os, set<T> &set_var)
    {
        os << "{";
        for (auto itr = set_var.begin(); itr != set_var.end(); itr++)
        {
            os << *itr;
            ++itr;
            if (itr != set_var.end())
                os << ", ";
            itr--;
        }
        os << "}";
        return os;
    }
} // namespace

namespace {
    using ull = unsigned long long;
    using ll = long long;
    using ld = long double;

    #define REP(i, n) for (ll i = 0; i < n; i++)
    #define REPR(i, n) for (ll i = n; i >= 0; i--)
    #define FOR(i, m, n) for (ll i = m; i < n; i++)
    #define even(x) (x) % 2 == 0
    #define odd(x) (x) % 2 != 0
    #define all(x) (x).begin(), (x).end()
    #define rall(x) (x).rbegin(), (x).rend()
    #define pcnt __builtin_popcount
    #define buli(x) __builtin_popcountll(x)
    #define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());
    #define inp(t, x) \
        t x;          \
        cin >> x;
    #define ithBit(n, i) ((n) >> (i)&1)
    #define INIT()               \
        cin.tie(0);              \
        ios::sync_with_stdio(0); \
        cout << fixed << setprecision(20)

    // these functions return the position of result of Binary Search.
    #define LB(s, t, x) (int)(lower_bound(s, t, x) - s)
    #define UB(s, t, x) (int)(upper_bound(s, t, x) - s)

    #define M_PI 3.14159265358979323846
    ll qp(ll a, ll b, int mo)
    {
        ll ans = 1;
        do
        {
            if (b & 1)
                ans = 1ll * ans * a % mo;
            a = 1ll * a * a % mo;
        } while (b >>= 1);
        return ans;
    }
    ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
    ll lcm(ll a, ll b)
    {
        ll temp = gcd(a, b);
        return temp ? (a / temp * b) : 0;
    }
    int mDays[] = {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
    int dx8[] = {1, -1, 0, 0, 1, 1, -1, -1}, dy8[] = {0, 0, -1, 1, -1, 1, -1, 1};

    template <typename F>
    class
    #if defined(__has_cpp_attribute) && __has_cpp_attribute(nodiscard)
        [[nodiscard]]
    #elif defined(__GNUC__) && __GNUC_PREREQ(3, 4)
        __attribute__((warn_unused_result))
    #endif // defined(__has_cpp_attribute) && __has_cpp_attribute(nodiscard)
        FixPoint : F {
            public :
                explicit constexpr FixPoint(F &&f) noexcept : F(std::forward<F>(f)) {}

            template <typename... Args>
            constexpr decltype(auto)
            operator()(Args &&... args) const {
                return F::operator()(*this, std::forward<Args>(args)...);
    } // namespace
    }
    ; // class FixPoint
    template <typename F>
    static inline constexpr decltype(auto)
    makeFixPoint(F &&f) noexcept
    {
        return FixPoint<F>{std::forward<F>(f)};
    }

    template <typename T>
    vector<T> make_v(size_t a) { return vector<T>(a); }
    template <typename T, typename... Ts>
    auto make_v(size_t a, size_t b, Ts... ts) { return vector<decltype(make_v<T>(b, ts...))>(a, make_v<T>(b, ts...)); }
    template <typename T, typename U, typename... V>
    typename enable_if<is_same<T, U>::value != 0>::type
    fill_v(U &u, const V... v) { u = U(v...); }
    template <typename T, typename U, typename... V>
    typename enable_if<is_same<T, U>::value == 0>::type
    fill_v(U &u, const V... v)
    {
        for (auto &e : u)
            fill_v<T>(e, v...);
    }

    template <class T>
    bool chmax(T &a, const T &b)
    {
        if (a < b)
        {
            a = b;
            return 1;
        }
        return 0;
    }
    template <class T>
    bool chmin(T &a, const T &b)
    {
        if (b < a)
        {
            a = b;
            return 1;
        }
        return 0;
    }

    inline bool rangeCheck2D(int nx, int ny, int Width, int Height) { return nx >= 0 and nx < Width and ny >= 0 and ny < Height; }

    int i_query(int a, int b)
    {
        cout << "? " << a << " " << b << endl;
        fflush(stdout);
        ll ret;
        cin >> ret;
        return ret;
    }

    void i_answer(vector<ll> ans)
    {
        cout << "! " << ans << endl;
        fflush(stdout);
    }
} // namespace

/*
    tuple binding
    auto [x, y] = make_tuple(0, 0);
    for pair
    auto [a, b] = pair<int, int>({v1, v2});

    bitset<N> bs(ini_val); // N must be constant
    bs.reset(); // reset all
*/

class ListG {
public:
    // there's directed edge between A and B
    // if to[A] has element B
    vector<vector<int>> to; 

    map<pair<int, int>, ll> cost;
    void setCost(int u, int v, ll c) { 
        cost[{min(u, v), max(u, v)}] = c;
    }
    ll getCost(int u, int v) {
        return cost[{min(u, v), max(u, v)}];
    }

    ListG(int s) : root(-1) {
        size = s;
        to = make_v<vector<int>>(size);
    }

    void setDirectedEdge(int f, int t) {
        to[f].push_back(t);
    }
    void setIndirectedEdge(int v1, int v2) {
        setDirectedEdge(v1, v2);
        setDirectedEdge(v2, v1);
    }

    void readGraph(int edgeNum, bool directed = false) {
        REP(i, edgeNum) {
            int u, v; cin >> u >> v; u--, v--;
            if (directed)
                setDirectedEdge(u, v);
            else
                setIndirectedEdge(u, v);
        }
    }

    void dfs(vector<char> &visiting, vector<char> &visited, int current, vector<vector<int>> &cloop) {
        for (auto&& next : to[current]) {
            if (visited[next]) continue;
            if (visiting[next]) {
                cloop[current].push_back(next);
                visited[next] = 1;
                dfs(visiting, visited, next, cloop);
                visited[next] = 0;
            } else {
                visiting[next] = 1;
                dfs(visiting, visited, next, cloop);
                visiting[next] = 0;
            }
        }
    }

    // return max depth
    int makeTree(int r) {
        root = r;
        p = make_v<int>(size);
        p[root] = -1;
        depth = make_v<int>(size);
        int maxDepth = 0;
        makeFixPoint([&](auto rec, int c, int d) -> void {
            depth[c] = d;
            chmax(maxDepth, d);
            REP(i, to[c].size()) {
                int next = to[c][i];
                if (p[c] == next) continue;
                p[next] = c;
                rec(next, d + 1);
            }
        })(root, 0);
        // count leaf node
        auto idxs = make_v<int>(size);
        iota(all(idxs), 0);
        leaf_idx = set<int>(all(idxs));
        REP(i, size) {
            if (i == root) continue;
            leaf_idx.erase(p[i]);
        }
        return maxDepth;
    }

    int diameterOfTree() {
        typedef pair<ll, int> Result;
        auto searchFarthest = makeFixPoint([&](auto searchFarthest, int p, int v) -> Result {
            Result r(0, v);
            for (const auto& next : to[v]) {
                if (next == p) continue;
                Result t = searchFarthest(v, next);
                t.first += 1;
                if (r.first < t.first)
                    r = t;
            }
            return r;
        });
        return searchFarthest(-1, searchFarthest(-1, 0).second).first;
    }

    pair<int, int> isBipartite() {
        auto color = make_v<int>(size);
        fill_v<int>(color, 0);

        auto rec = makeFixPoint([&](auto rec, int v, int c) -> bool {
            color[v] = c;
            for (const auto& next : to[v]) {
                if (color[next] == c)
                    return false;
                if (color[next] == 0 and not rec(next, -c))
                    return false;
            }
            return true;
        });

        pair<int, int> ret = {-1, -1};
        REP(i, size) {
            if (color[i] == 0)
                if (not rec(i, 1))
                    return ret;
        }
        ret = {0, 0};
        REP(i, size) {
            if (color[i] > 0) ret.first++;
            else ret.second++;
        }
        return ret;
    }

    void makeEulerTour() {
        assert(root >= 0);
        et_begin = make_v<int>(size);
        et_end = make_v<int>(size);
        tmp_k = 0;
        etdfs(root, -1);
    }

    vector<vector<int>> children() {
        assert(root >= 0);
        auto ret = make_v<vector<int>>(size);
        REP(i, size) {
            int prt = p[i];
            if (prt == -1) continue;
            ret[prt].push_back(i);
        }
        return ret;
    }

    // https://www.geeksforgeeks.org/strongly-connected-components/
    int stronglyConnectedConponent() {
        auto rto = make_v<vector<int>>(size);
        REP(from, size) {
            for (auto&& t : to[from])
                rto[t].push_back(from);
        }
        auto cmp = make_v<int>(size);
        fill_v<int>(cmp, 0);
        auto used = make_v<char>(size);
        fill_v<char>(used, 0);
        vector<int> rets; // return index in order
        REP(i, size) {
            makeFixPoint([&](auto dfs, int v) -> void {
                if (used[v]) return;
                used[v] = 1;
                for (auto&& t : to[v])
                    dfs(t);
                rets.push_back(v);
            })(i);
        }
        fill_v<char>(used, 0);
        int ret = 0;
        REPR(i, rets.size()-1) {
            makeFixPoint([&](auto rdfs, int v, int k) -> void {
                if (used[v]) return;
                used[v] = 1;
                cmp[v] = k;
                for (auto&& rt : rto[v])
                        rdfs(rt, k);
                
                rets.push_back(v);
            })(rets[i], ret++);
        }
        return ret;
    }

    vector<int> topologicalSorted() {
        vector<int> ret;
        auto used = make_v<char>(size);
        fill_v<char>(used, 0);
        REP(i, size) {
            makeFixPoint([&](auto dfs, int v) -> void {
                if (used[v]) return;
                used[v] = 1;
                for (auto&& t : to[v]) 
                    dfs(t);
                ret.push_back(v);
            })(i);
        }
        reverse(all(ret));
        return ret;
    }

    void dfsTree(ListG& dfst) {
        auto visited = make_v<char>(size);
        auto prt = make_v<int>(size);
        fill_v<char>(visited, 0);
        fill_v<int>(prt, 0);
        stack<int> st;
        st.push(0);
        while (st.size()) {
            int c = st.top(); st.pop();
            if (visited[c]) continue;
            visited[c] = 1;
            if (c != 0) dfst.setIndirectedEdge(c, prt[c]);
            for (const auto& next : to[c]) {
                prt[next] = c;
                st.push(next);
            }
        }
    }

    int size, root;
    vector<int> p; // parent for each node. parent of root = -1
    vector<int> depth; // for each node. depth of root node = 0
    vector<int> euler_tour;
    vector<int> et_begin, et_end;
    set<int> leaf_idx;

    int tmp_k;
private:
    void etdfs(int vidx, int pidx) {
        et_begin[vidx] = tmp_k;
        euler_tour.push_back(vidx);
        tmp_k++;
        REP(i, to[vidx].size()) {
            if (to[vidx][i] != pidx) {
                etdfs(to[vidx][i], vidx);
                euler_tour.push_back(vidx);
                tmp_k++;
            }
        }
        et_end[vidx] = tmp_k;
    }
};

int main(void)
{
    INIT(); // comment out for Interective Problem
    
    int N, M, start, goal; cin >> N >> M;

    ListG lg(N);
    REP(i, M) {
        int u, v;cin >> u >> v; u--, v--;
        lg.setDirectedEdge(u, v);
    }    
    cin >> start >> goal;
    start--, goal--;

    auto cost = make_v<ll>(N, 3);
    fill_v<ll>(cost, -1);

    queue<pair<int, int>> q;
    q.push({start, 0});
    while (q.size()) {
        int c = q.front().first;
        int d = q.front().second; q.pop();
        for (const auto& next : lg.to[c]) {
            int nd = (d + 1) % 3;
            if (cost[next][nd] != -1) continue;
            q.push({next, d + 1});
            cost[next][nd] = d + 1;
        }
    }
    
    if (cost[goal][2] == -1) cout << -1 << endl;
    else cout << cost[goal][0] / 3 << endl;


    return 0;
}
//*/

Measured memory_bytes: 11264