////////////////////////////////////////
///  tu3 pro-con template            ///
////////////////////////////////////////
#include "bits/stdc++.h"
using namespace std;

// -- typedefs -- //
#define EPS 1e-9
typedef long long llong;

// -- loop macros -- //
#define REP(i,n) for (auto i = decltype(n)(0); i < (n); i++)
#define RREP(i,n) for (auto i = (n)-1; i >= 0; i--)
#define FOR(i,s,n) for (auto i = (s); i < (n); i++)
#define FORR(i,s,n) for (auto i = (n)-1; i >= (s); i--)
#define FORE(exp) for (auto && exp)
#define allof(c) c.begin(), c.end()
#define partof(c,s,e) c.begin() + (s), c.begin() + (e)

// -- functors -- //
#define PREDICATE(t,a,...) [&](const t & a) -> bool { return __VA_ARGS__; }
#define PRED(a,...) PREDICATE(auto,a,__VA_ARGS__)
#define COMPARISON(t,a,b,...) [&](const t & a, const t & b) -> bool { return __VA_ARGS__; }
#define COMP(a,b,...) COMPARISON(auto,a,b,__VA_ARGS__)
#define CONV1(a,...) [&](const auto & a) -> auto { return __VA_ARGS__; }
#define CONV2(a,b,...) [&](const auto & a, const auto & b) -> auto { return __VA_ARGS__; }
#define CONV3(a,b,c,...) [&](const auto & a, const auto & b, const auto & c) -> auto { return __VA_ARGS__; }

// -- I/O Helper -- //
struct _Reader { istream& cin; template <class T> _Reader operator ,(T& rhs) { cin >> rhs; return *this; } };
struct _Writer { ostream& cout; const char* d{ " " }; bool f{}; template <class T> _Writer operator ,(const T& rhs) { cout << (f ? d : "") << rhs; f = 1; return *this; } };
#define READ(t,...) t __VA_ARGS__; (_Reader{cin}), __VA_ARGS__
#define WRITE(...) do { (_Writer{cout}), __VA_ARGS__; cout << endl; } while (false)
#define WRITELN(...)  do { (_Writer{cout, "\n"}), __VA_ARGS__; cout << endl; } while (false)
#ifdef _DEBUG
#define DEBUG(...) (_Writer{cerr}), "DEBUG -> ", __VA_ARGS__, "\n"
#else
#define DEBUG(...)
#endif

// -- vevector -- //
template <class T> struct vevector : vector<vector<T>> { vevector(size_t n = 0, size_t m = 0, const T & initial = T()) : vector<vector<T>>(n, vector<T>(m, initial)) { } };
template <class T> struct vevevector : vector<vevector<T>> { vevevector(size_t n = 0, size_t m = 0, size_t l = 0, const T & initial = T()) : vector<vevector<T>>(n, vevector<T>(m, l, initial)) { } };
template <class T> struct vevevevector : vector<vevevector<T>> { vevevevector(size_t n = 0, size_t m = 0, size_t l = 0, size_t k = 0, const T & initial = T()) : vector<vevevector<T>>(n, vevevector<T>(m, l, k, initial)) { } };

namespace std {
	template <class T1, class T2> istream& operator >> (istream& in, pair<T1, T2>& p) { in >> p.first >> p.second; return in; }
	template <class T1, class T2> ostream& operator << (ostream& out, const pair<T1, T2>& p) { out << p.first << " " << p.second; return out; }
}

template <class T> T read() { T t; cin >> t; return t; }
template <class T> vector<T> read(int n) { vector<T> v; REP(i, n) { v.push_back(read<T>()); } return v; }
template <class T> vevector<T> read(int n, int m) { vevector<T> v; REP(i, n) v.push_back(read<T>(m)); return v; }
template <class T> vector<T> readjag() { return read<T>(read<int>()); }
template <class T> vevector<T> readjag(int n) { vevector<T> v; REP(i, n) v.push_back(readjag<T>()); return v; }

template <class T> struct iter_range_t { T beg, end; };
template <class T> iter_range_t<T> iter_range(T beg, T end) { return iter_range_t<T>{beg, end}; }
template <class T> ostream& operator << (ostream& out, iter_range_t<T> v) { if (v.beg != v.end) { out << *v.beg++; while (v.beg != v.end) { out << " " << *v.beg++; } } return out; }
template <class T> ostream& operator << (ostream& out, const vector<T>& v) { return out << iter_range(allof(v)); }

// -- etc -- //
template <class T> T infinity_value();
template <> int infinity_value<int>() { return int(1) << 28; }
template <> llong infinity_value<llong>() { return llong(1) << 60; }
template <> double infinity_value<double>() { return 1e+300 * 1e+300; }
#define INF(T) infinity_value<T>()

inline int sign_of(double x) { return (abs(x) < EPS ? 0 : x > 0 ? 1 : -1); }
template <class TInt> bool in_range(TInt val, TInt min, TInt max) { return val >= min && val < max; }
template <> bool in_range<double>(double val, double min, double max) { return val - min > -EPS && val - max < EPS; }
template <class TInt> bool in_range2d(TInt x, TInt y, TInt w, TInt h) { return x >= 0 && x < w && y >= 0 && y < h; }
vector<int> iotavn(int start, int count) { vector<int> r(count); iota(allof(r), start);	return r; }


//// start up ////
void solve();
int32_t main()
{
	//auto classic_table = ctype<char>::classic_table();
	//vector<ctype<char>::mask> ctable(classic_table, classic_table + ctype<char>::table_size);
	//ctable['-'] |= ctype_base::space; // as delimitor
	//cin.imbue(locale(cin.getloc(), new ctype<char>(ctable.data())));

	cin.tie(nullptr);
	ios_base::sync_with_stdio(false);
	cout << fixed;
	cout << setprecision(std::numeric_limits<double>::max_digits10);
	solve();

	return 0;
}

////////////////////
//// template end
////////////////////

// -- ダイクストラ法 -- //
// O(E+VlogV)
template <class TCost>
struct DijkstraResult
{
	int start;
	int goal;
	vector<int> parentNode;
	vector<int> parentEdge;
	vector<TCost> costToNode;

	vector<int> BuildPath()
	{
		assert(goal != -1);
		vector<int> result;
		int cur = goal;
		while (cur != start)
		{
			result.push_back(cur);
			cur = parentNode[cur];
		}
		result.push_back(start);
		return result;
	}
};

template <class TCost>
struct Edge
{
	int from;
	int to;
	TCost cost;
	int edgeId;

	bool operator < (const Edge& rhs) const { return cost < rhs.cost; }
	bool operator > (const Edge& rhs) const { return cost > rhs.cost; }
};

template <class TCost>
DijkstraResult<TCost> Dijkstra(const vevector<Edge<TCost>>& g, int start = 0, int goal = -1)
{
	typedef Edge<TCost> E;

	int N = g.size();
	priority_queue<E, vector<E>, greater<E>> q;

	q.push(E{ start, start, 0 });

	vector<int> prev(N, -1);
	vector<int> prevEdge(N, -1);
	vector<TCost> cost(N, INF(TCost));
	while (!q.empty())
	{
		E p = q.top(); q.pop();
		if (prev[p.to] != -1) continue;
		prev[p.to] = p.from;
		prevEdge[p.to] = p.edgeId;
		cost[p.to] = p.cost;
		if (p.to == goal) { break; }

		for (const E& e : g[p.to])
		{
			if (prev[e.to] == -1)
			{
				q.push(E{ e.from, e.to, e.cost + p.cost, e.edgeId });
			}
		}
	}
	return DijkstraResult<TCost> { start, goal, prev, prevEdge, cost };
}



void solve()
{
	READ(int, N, M);
	typedef Edge<llong> E;
	vevector<E> g(3 * N);

	REP(i, M)
	{
		READ(int, u, v);
		u--;
		v--;
		g[0 * N + u].push_back(E{ 0 * N + u, 1 * N + v, 0 });
		g[1 * N + u].push_back(E{ 1 * N + u, 2 * N + v, 0 });
		g[2 * N + u].push_back(E{ 2 * N + u, 0 * N + v, 1 });
	}

	READ(int, S, T);
	S--;
	T--;

	auto ans = Dijkstra(g, S, T);
	WRITE(ans.costToNode[T] >= INF(llong) ? -1 : ans.costToNode[T]);
}


Measured memory_bytes: 25984