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

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; }


// std::vector Declaration
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,Ts... ts) {
    return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

// std::vector Initialization
template<typename T>
void fill_all(T& arr, const T& v) { arr = v; }
template<typename T, typename U>
void fill_all(T& arr, const U& v) { for (auto& i : arr) fill_all(i, v); }

// std::vector Debug
template<typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "[";
    bool a = 1;
    for (auto e : v ) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::pair Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << " " << p.second << ")";
    return os;
}

// std::set Debug
template<typename T>
ostream& operator<<(ostream& os, const set<T>& st) {
    os << "{";
    bool a = 1;
    for (auto e : st) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "}";
    return os;
}

// std::multiset Debug
template<typename T>
ostream& operator<<(ostream& os, const multiset<T>& st) {
    os << "{";
    bool a = 1;
    for (auto e : st) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "}";
    return os;
}

// std::map Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const map<T, U>& mp) {
    os << "{";
    bool a = 1;
    for (auto e : mp) {
        os << (a ? "" : " ");
        os << e.first << ":" << e.second;
        a = 0;
    }
    os << "}";
    return os;
}

// std::tuple Debug
template<int N, class Tuple>
void out(ostream& os, const Tuple& t){}
template<int N, class Tuple, class H, class ...Ts>
void out(ostream& os, const Tuple& t) {
    if (N) os << " ";
    os << get<N>(t);
    out<N+1,Tuple,Ts...>(os, t);
}
template<class ...Ts>
ostream& operator<<(ostream& os, const tuple<Ts...>& t) {
    os << "(";
    out<0,tuple<Ts...>,Ts...>(os, t);
    os << ")";
    return os;
}

// Debug
#define DUMP(x) cerr<<#x<<" = "<<(x)<<endl


struct edge { int to, cost; };
ostream& operator<<(ostream& os, const edge& e) {
    os << "(" << e.to << ", " << e.cost << ")";
    return os;
}

const LL LINF = 1LL<<60;
const int IINF = 1<<30;
const LL MOD = 1e9+7;

template<typename T>
void dijkstra(auto& G, vector<T>& d, int s)
{
    using P = pair<T, int>;
    priority_queue<P, vector<P>, greater<P> > que;

    d.resize(G.size());
    fill(d.begin(), d.end(), IINF);
    d[s] = 0;

    que.push({ 0, s });

    while(!que.empty())
    {
        T temp_cost = que.top().first;
        int from = que.top().second;
        que.pop();

        if (d[from] < temp_cost) continue;

        for (auto e : G[from])
        {
            if (d[e.to] > d[from] + e.cost) {
                d[e.to] = d[from] + e.cost;
                que.push({ d[e.to], e.to });
            }
        }
    }
}

int main()
{
    int n, m; cin >> n >> m;
    vector<vector<edge>> G(3*n);
    for (int i = 0; i < m; ++i) {
        int u, v; cin >> u >> v; --u; --v;
        G[u].push_back((edge){v+n, 1});
        G[u+n].push_back((edge){v+2*n, 1});
        G[u+2*n].push_back((edge){v, 1});
    }
    int s, t; cin >> s >> t; --s; --t;

    vector<int> d;

    dijkstra(G, d, s);

    if (d[t] == IINF) {
        cout << -1 << endl;
    } else {
        cout << d[t] / 3 << endl;
    }

    return 0;
}


Measured memory_bytes: 17792