#include <bits/stdc++.h>
#include <boost/multiprecision/cpp_int.hpp>
using namespace std;

//#define int long long
//using ll = boost::multiprecision::cpp_int;
using ll = long long;
//constexpr int INF = 1e9;//INT_MAX=(1<<31)-1=2147483647
constexpr ll INF = (ll)1e18;//(1LL<<63)-1=9223372036854775807
constexpr ll MOD = (ll)1e9 + 7;
constexpr double EPS = 1e-9;
constexpr int dx[4]={1,0,-1,0};
constexpr int dy[4]={0,1,0,-1};
#ifdef LOCAL_ENV
	#define debug(var) std::cout<<#var" = "<<var<<std::endl
#else
	#define debug(var)
#endif
#define p(var) std::cout<<var<<std::endl
#define rep(i, n)   for(ll i=0, i##_length=(n); i< i##_length; ++i)
#define repeq(i, n) for(ll i=1, i##_length=(n); i<=i##_length; ++i)
#define all(a) (a).begin(), (a).end()
#define PI (acos(-1))
template<typename T> inline T power(T x, T n){ return n ? power(x*x%MOD,n/2)*(n%2?x:1)%MOD : 1; }
template<typename T> inline T gcd(T a, T b) { return b ? gcd(b,a%b) : a; }
template<typename T> inline T lcm(T a, T b) { return a / gcd(a,  b) * b; }
template<typename T1, typename T2>inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template<typename T1, typename T2>inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }
template<typename T1, typename T2> ostream& operator<<(ostream& s, const pair<T1, T2>& p) {return s << "(" << p.first << ", " << p.second << ")";}
template<typename T> ostream& operator<<(ostream& s, const vector<T>& v) {
	for (int i = 0, len = v.size(); i < len; ++i){
		s << v[i]; if (i < len - 1) s << "\t";
	}
	return s;
}
template<typename T> ostream& operator<<(ostream& s, const vector< vector<T> >& vv) {
	for (int i = 0, len = vv.size(); i < len; ++i){
		s << vv[i] << endl;
	}
	return s;
}
template<typename T1, typename T2> ostream& operator<<(ostream& s, const map<T1, T2>& m) {
	s << "{" << endl;
	for (typeof(m.begin()) itr = m.begin(); itr != m.end(); ++itr){
		s << "\t" << (*itr).first << " : " << (*itr).second << endl;
	}
	s << "}" << endl;
	return s;
}

/*-----8<-----8<-----*/


class Edge {
public:
	ll from,to,cost;
	Edge() {}
	Edge(ll from, ll to, ll cost) : from(from), to(to), cost(cost) {}
	bool operator < (const Edge &another) const {
		return cost != another.cost ? (cost > another.cost) : 
			(from != another.from ? from < another.from : to < another.to);
	}
};

/*
引数
 start:探索するスタートノード番号
 node_size:ノードの数、0〜(node_size-1)がノード番号として定義される
戻り値
　dist:スタートノードから各頂点までの距離
　prev:最短路木の親頂点
*/
void dijkstra(const vector<vector<Edge>> &g, ll start, vector<ll> &dist, vector<ll> &prev) {
	ll gsize = g.size();
	dist.assign(gsize, INF); dist[start] = 0;
	prev.assign(gsize, -1);
	
	priority_queue<Edge> que;
	que.push(Edge(-INF, start, 0));
	while (!que.empty()) {
		Edge e = que.top();
		que.pop();
		if (prev[e.to] != -1) continue;
		prev[e.to] = e.from;
		for(auto f=(g[e.to]).begin(); f!=(g[e.to]).end(); f++){
			if (dist[f->to] > e.cost + f->cost) {
				dist[f->to] = e.cost + f->cost;
				que.push(Edge(f->from, f->to, e.cost+f->cost));
			}
		}
	}
}
//最短路木の親頂点を元にstart->goalの経路を作成
vector<ll> buildPath(const vector<ll> &prev, ll goal) {
	vector<ll> path;
	for (ll u = goal; u >= 0; u = prev[u])
		path.push_back(u);
	reverse(path.begin(), path.end());
	return path;
}


constexpr ll N_MAX = 100000;

ll N, M;
ll S, T;


using Graph = vector<vector<ll>>;
vector<pair<ll,ll>> a;




void input() {
	scanf("%lld%lld", &N, &M);
	vector<vector<Edge>> g(N*3,vector<Edge>());
	rep(i,M){
		ll from,to;
		cin >> from >> to;
		from--;to--;
		g[from*3].push_back(Edge(from*3,to*3+1,1));
		g[from*3+1].push_back(Edge(from*3+1,to*3+2,1));
		g[from*3+2].push_back(Edge(from*3+2,to*3,1));
	}
	scanf("%lld%lld", &S, &T);
	S--;T--;

	vector<ll> dist, prev;
	dijkstra(g,S*3,dist,prev);
	debug(dist);
	if(dist[T*3]<INF){
		p(dist[T*3]/3);
	}else{
		p(-1);
	}


}

signed main() {
	input();

	return 0;
}


Measured memory_bytes: 21376