/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author champon
 */

//<editor-fold desc="definitions">
#include <bits/stdc++.h>
#define se cout << "test ok" << endl;
#define sp << " " <<
#define enl "\n"
using namespace std;
using ll=long long;
using ld=long double;
using vi = vector<int>;
using vii = vector<vector<int>>;
using viii = vector<vector<vector<int>>>;
using vl = vector<ll>;
using vll = vector<vector<ll>>;
using vlll = vector<vector<vector<ll>>>;
using vc = vector<char>;
using vcc = vector<vector<char>>;
using pi = pair<int, int>;
using pl = pair<ll, ll>;
ll mod = ll(1e9)+7;
ll inf = ll(1e18);
void bl(bool b, ostream& out=cout){ out << (b ? "Yes" : "No") << endl; }
void bl2(bool b, ostream& out=cout){ out << (b ? "YES" : "NO") << endl; }
template<typename T> inline bool chmax(T &a, T b){ if(a<b){a=b; return true;} return false; }
template<typename T> inline bool chmin(T &a, T b){ if(a>b){a=b; return true;} return false; }
int dx[] = {1, 0, -1, 0, 1, -1, 1, -1};
int dy[] = {0, 1, 0, -1, 1, -1, -1, 1};

#ifndef INCLUDE_DEBUG_HPP
#define INCLUDE_DEBUG_HPP

#define TO_STRING(varName) # varName
#include <iostream>
#include <vector>
#include <map>
using namespace std;

namespace dbg {
    using ll = long long;

    class Debug {
        void prefix() { cout << "\033[7m\033[35m" << " DEBUG " << "\033[0m" << endl; }

        void out_helper(){ cout << endl; }

        void out_with_name_helper(){ cout << endl; }

        template<typename T1, typename... T2>
        void out_helper(T1 v, T2... args);

        template<typename T1, typename... T2>
        void out_with_name_helper(string s, T1 v, T2... args);

        // value
        template<typename T>
        void print(T val);

        // pair
        template<typename A, typename B>
        void print(pair<A, B> p);

        // tuple
        template<typename A, typename B, typename C>
        void print(tuple<A, B, C> t);

        // vector
        template<typename T>
        void print(vector<T> &vec);

        // set
        template<typename T>
        void print(set<T> &st);

        // map
        template<typename A, typename B>
        void print(map<A, B> mp);
    public:
        Debug(){}

        template<typename... T>
        void out(T... args){
            prefix();
            out_helper(args...);
        }

        template<typename... T>
        void out_with_name(T... args){
            prefix();
            out_with_name_helper(args...);
        }

        template<typename T>
        void outg(vector<vector<T>> &g) {
            prefix();
            for(auto& v1 : g){
                for(auto& v2 : v1) {
                    cout << v2 << " ";
                }
                cout << endl;
            }
        }
    };

    template<typename T1, typename... T2>
    void Debug::out_helper(T1 v, T2... args) {
        print(v); cout << endl;
        out_helper(args...);
    }

    template<typename T1, typename... T2>
    void Debug::out_with_name_helper(string s, T1 v, T2... args) {
        cout << s << ": "; print(v); cout << endl;
        out_with_name_helper(args...);
    }

    template<typename T>
    void Debug::print(T val){
        cout << val;
    }

    template<typename A, typename B>
    void Debug::print(pair<A, B> p){
        cout << "("; print(p.first); cout << ", "; print(p.second); cout << ")";
    }

    template<typename A, typename B, typename C>
    void Debug::print(tuple<A, B, C> t) {
        cout << "("; print(get<0>(t)); cout << ", "; print(get<1>(t)); cout << ", "; print(get<2>(t)); cout << ")";
    }

    template<typename T>
    void Debug::print(vector<T>& vec) {
        cout << "[";
        bool fir = true;
        for(auto& e : vec) {
            if(!fir) cout << " ";
            print(e), fir=false;
        }
        cout << "]";
    }

    template<typename T>
    void Debug::print(set<T> &st){
        cout << "{";
        bool fir = true;
        for(auto& e : st) {
            if(!fir) cout << " ";
            print(e), fir=false;
        }
        cout << "}";
    }

    template<typename A, typename B>
    void Debug::print(map<A, B> mp){
        cout << "{";
        bool fir = true;
        for(auto& p : mp){
            if(!fir) cout << " ";
            print(p), fir=false;
        }
        cout << "}";
    }

}

#endif //INCLUDE_DEBUG_HPP

dbg::Debug debug;
//</editor-fold>

class EHopscotchAddict {
public:
    int n, m, s, t;
    vii g;
    vii dist;

	void solve(std::istream& in, std::ostream& out){
	    in >> n >> m;
	    g = vii(n);
	    for(int i=0; i<m; i++){
	        int u, v;
	        in >> u >> v;
	        --u; --v;
	        g[u].push_back(v);
	    }
	    in >> s >> t;
	    --s; --t;

	    dist = vii(n, vi(3, 1e9));
	    dist[s][0] = 0;
	    queue<pi> q;
	    q.push(make_pair(s, 0));
	    while(!q.empty()){
	        pair<int, int> p = q.front();
	        q.pop();
	        int from = p.first;
	        int np = (p.second+1)%3;
	        for(auto to : g[from]) {
                if(dist[to][np] > dist[from][p.second] + 1) {
                    dist[to][np] = dist[from][p.second] + 1;
                    q.push(make_pair(to, np));
                }
	        }
	    }

        if(dist[t][0] == 1e9) out << -1 << endl;
        else out << dist[t][0]/3 << endl;
	}
};


int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
	EHopscotchAddict solver;
	std::istream& in(std::cin);
	std::ostream& out(std::cout);
	solver.solve(in, out);
	return 0;
}


Measured memory_bytes: 11264