#include <bits/stdc++.h>

#ifdef _DEBUG
#define debug(x) cerr << "line: " << __LINE__ << ", func: " << __func__ << " ->  " << #x << " = " << x << endl
#else
#define debug(x)
#endif

#define all(s) begin(s), end(s)
#define rall(s) rbegin(s), rend(s)
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = ((a)-1); i >= (b); i--)
#define pb push_back
#define sz(a) int((a).size())
#define fi first
#define se second

using namespace std;

using ll = long long;
using ull = unsigned long long;
using i_i = pair<int, int>;
using ll_ll = pair<ll, ll>;
using d_ll = pair<double, ll>;
using ll_d = pair<ll, double>;
using d_d = pair<double, double>;
template <class T> using vec = vector<T>;

static constexpr ll LL_INF = 1LL << 60;
static constexpr int I_INF = 1 << 28;
static constexpr double PI = static_cast<double>(3.14159265358979323846264338327950288);
static constexpr double EPS = numeric_limits<double>::epsilon();

static map<type_index, const char* const> scanType = {
    {typeid(int), "%d"}, {typeid(ll), "%lld"}, {typeid(double), "%lf"}, {typeid(char), "%c"}};

template <class T> static void scan(vector<T>& v);
[[maybe_unused]] static void scan(vector<string>& v, bool isWord = true);
template <class T> static inline bool chmax(T& a, T b);
template <class T> static inline bool chmin(T& a, T b);
template <class A, size_t N, class T> static void Fill(A (&arr)[N], const T& val);

template <class T> struct Edge {
  int src, to;
  T cost;

  Edge(int to, T cost) : src(-1), to(to), cost(cost) {}
  Edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}

  Edge& operator=(const int& x) {
    to = x;
    return *this;
  }

  operator int() const { return to; }
};

template <class T> using Edges = vector<Edge<T>>;
template <class T> using WeightedGraph = vector<Edges<T>>;
using UnWeightedGraph = vector<vector<int>>;
template <class T> using Matrix = vector<vector<T>>;

// dijkstra (route restoration)
template <class T> vector<T> dijkstra(int s, WeightedGraph<T>& adj_list, T inf) {
  int si = sz(adj_list);
  vector<T> dist(si, inf);

  using Pi = pair<T, int>;
  priority_queue<Pi, vector<Pi>, greater<Pi>> que;
  dist[s] = 0;
  que.emplace(dist[s], s);
  while (!que.empty()) {
    T cost;
    int idx;
    tie(cost, idx) = que.top();
    que.pop();
    if (dist[idx] < cost) continue;
    for (auto& e : adj_list[idx]) {
      auto next_cost = cost + e.cost;
      if (dist[e.to] <= next_cost) continue;
      dist[e.to] = next_cost;
      que.emplace(dist[e.to], e.to);
    }
  }
  return dist;
}

int main(int argc, char* argv[]) {
  ll n, m, s, t;
  cin >> n >> m;
  vec<ll> u(m), v(m);
  WeightedGraph<ll> adj(n * 3);
  rep(i, 0, m) {
    scanf("%lld %lld", &u[i], &v[i]);
    u[i]--, v[i]--;
    adj[u[i] * 3].emplace_back(v[i] * 3 + 1, 1);
    adj[u[i] * 3 + 1].emplace_back(v[i] * 3 + 2, 1);
    adj[u[i] * 3 + 2].emplace_back(v[i] * 3, 1);
  }
  cin >> s >> t;
  s--, t--;
  s *= 3, t *= 3;

  auto s_cost = dijkstra(s, adj, LL_INF);

  if (s_cost[t] == LL_INF) {
    cout << -1 << endl;
    return 0;
  }

  cout << s_cost[t] / 3 << endl;
  return 0;
}

template <class T> static void scan(vector<T>& v) {
  auto tFormat = scanType[typeid(T)];
  for (T& n : v) {
    scanf(tFormat, &n);
  }
}

static void scan(vector<string>& v, bool isWord) {
  if (isWord) {
    for (auto& n : v) {
      cin >> n;
    }
    return;
  }

  int i = 0, size = v.size();
  string s;
  getline(cin, s);

  if (s.size() != 0) {
    i++;
    v[0] = s;
  }

  for (; i < size; ++i) {
    getline(cin, v[i]);
  }
}

template <class T> inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}

template <class T> inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}

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


Measured memory_bytes: 20608