#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
#include <iostream>
#include <random>
#include <unordered_map>
#include <unordered_set>
#include <immintrin.h>
#ifdef _MSC_VER
#include <ppl.h>
#endif

using namespace std;

//呪文
#define DUMPOUT std::cerr
#define dump(...) DUMPOUT<<"  ";DUMPOUT<<#__VA_ARGS__<<" :["<<__LINE__<<":"<<__FUNCTION__<<"]"<<std::endl;DUMPOUT<<"    ";dump_func(__VA_ARGS__)

typedef unsigned uint; typedef long long ll; typedef unsigned long long ull; typedef pair<int, int> pii; typedef pair<ll, ll> pll; typedef pair<double, double> pdd; typedef pair<string, string> pss;
template <typename _KTy, typename _Ty> ostream& operator << (ostream& o, const pair<_KTy, _Ty>& m) { o << "{" << m.first << ", " << m.second << "}"; return o; }
template <typename _KTy, typename _Ty> ostream& operator << (ostream& o, const map<_KTy, _Ty>& m) { if (m.empty()) { o << "{ }"; return o; } o << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _KTy, typename _Ty> ostream& operator << (ostream& o, const unordered_map<_KTy, _Ty>& m) { if (m.empty()) { o << "{ }"; return o; } o << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const vector<_Ty>& v) { if (v.empty()) { o << "{ }"; return o; } o << "{" << v.front(); for (auto itr = ++v.begin(); itr != v.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const set<_Ty>& s) { if (s.empty()) { o << "{ }"; return o; } o << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const unordered_set<_Ty>& s) { if (s.empty()) { o << "{ }"; return o; } o << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { o << ", " << *itr; }	o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const stack<_Ty>& s) { if (s.empty()) { o << "{ }"; return o; } stack<_Ty> t(s); o << "{" << t.top(); t.pop(); while (!t.empty()) { o << ", " << t.top(); t.pop(); } o << "}";	return o; }
template <typename _Ty> ostream& operator << (ostream& o, const list<_Ty>& l) { if (l.empty()) { o << "{ }"; return o; } o << "{" << l.front(); for (auto itr = ++l.begin(); itr != l.end(); ++itr) { o << ", " << *itr; } o << "}"; return o; }
template <typename _KTy, typename _Ty> istream& operator >> (istream& is, pair<_KTy, _Ty>& m) { is >> m.first >> m.second; return is; }
template <typename _Ty> istream& operator >> (istream& is, vector<_Ty>& v) { for (size_t i = 0; i < v.size(); i++) is >> v[i]; return is; }
namespace aux { // print tuple
	template<typename Ty, unsigned N, unsigned L> struct tp { static void print(ostream& os, const Ty& v) { os << get<N>(v) << ", "; tp<Ty, N + 1, L>::print(os, v); } };
	template<typename Ty, unsigned N> struct tp<Ty, N, N> { static void print(ostream& os, const Ty& v) { os << get<N>(v); } };
}
template<typename... Tys> ostream& operator<<(ostream& os, const tuple<Tys...>& t) { os << "{"; aux::tp<tuple<Tys...>, 0, sizeof...(Tys) - 1>::print(os, t); os << "}"; return os; }

template<typename A, size_t N, typename T> inline void Fill(A(&array)[N], const T &val) { std::fill((T*)array, (T*)(array + N), val); }

void dump_func() { DUMPOUT << std::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<typename Ty>Ty modpow(Ty n, Ty e, Ty m) { Ty result = 1; while (e > 0) { if (e & 1)result = (result*n) % m; e >>= 1; n = (n*n) % m; }return result; }


#define PI 3.14159265358979323846
#define EPS 1e-10
#define FOR(i,a,n) for(int i=(a);i<(n);++i)
#define REP(i,n)  FOR(i,0,n)
#define all(j) (j).begin(), (j).end()
#define SZ(j) ((int)(j).size())
#define fake false



bool reach(const vector<vector<int>>& G, int S, int T) {
  int N = G.size();

  const int INF = INT_MAX / 8;

  vector<int> d(N, INF);
  vector<bool> used(N, false);

  priority_queue<pii, vector<pii>, greater<pii>> pq;
  pq.emplace(0, S);
  d[S] = 0;
  while (!pq.empty()) {
    int mincost, u;
    tie(mincost, u) = pq.top(); pq.pop();

    if (d[u] < mincost) continue;

    for (const auto& v : G[u]) {
      if (d[u] + 1 < d[v]) {
        d[v] = d[u] + 1;
        pq.emplace(d[v], v);
      }
    }
  }

  return d[T] != INF;
}

int solve(const vector<vector<int>>& G, int S, int T) {
  int N = G.size();

  const int INF = INT_MAX / 8;

  vector<vector<int>> d(N, vector<int>(3, INF));

  queue<pii> qu;
  qu.emplace(0, S);
  d[S][0] = 0;
  while (!qu.empty()) {
    int cost, u;
    tie(cost, u) = qu.front(); qu.pop();

    if (d[u][cost % 3] < cost) continue;

    cost++;

    for (const auto& v : G[u]) {
      if (cost < d[v][cost % 3]) {
        if (v == T && cost % 3 == 0) {
          return cost / 3;
        }
        d[v][cost % 3] = cost;
        qu.emplace(cost, v);
      }
    }
  }
  return -1;
}

int main() {

  cin.tie(0);
  ios::sync_with_stdio(false);

  int N, M;
  cin >> N >> M;
  vector<vector<int>> G(N);
  REP(i, M) {
    int u, v;
    cin >> u >> v;
    u--; v--;
    G[u].push_back(v);
  }
  int S, T;
  cin >> S >> T;
  S--; T--;

  if (!reach(G, S, T)) {
    cout << -1 << endl;
    return 0;
  }

  cout << solve(G, S, T) << endl;

	return 0;
}


Measured memory_bytes: 11256