//#define NDEBUG
#include <cstddef>
#include <cstdint>
#include <vector>

namespace n91 {

using i8 = std::int_fast8_t;
using i32 = std::int_fast32_t;
using i64 = std::int_fast64_t;
using u8 = std::uint_fast8_t;
using u32 = std::uint_fast32_t;
using u64 = std::uint_fast64_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

constexpr usize operator"" _z(unsigned long long x) noexcept {
  return static_cast<usize>(x);
}

class rep {
  const usize f, l;

public:
  class itr {
    friend rep;
    usize i;
    constexpr itr(const usize x) noexcept : i(x) {}

  public:
    void operator++() noexcept { ++i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  constexpr rep(const usize first, const usize last) noexcept
      : f(first), l(last) {}
  constexpr itr begin() const noexcept { return itr(f); }
  constexpr itr end() const noexcept { return itr(l); }
};
class revrep {
  const usize f, l;

public:
  class itr {
    friend revrep;
    usize i;
    constexpr itr(usize x) noexcept : i(x) {}

  public:
    void operator++() noexcept { --i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  constexpr revrep(usize first, usize last) noexcept : f(--first), l(--last) {}
  constexpr itr begin() const noexcept { return itr(l); }
  constexpr itr end() const noexcept { return itr(f); }
};
template <class T> using vec_alias = std::vector<T>;
template <class T> auto md_vec(const usize n, const T &value) {
  return std::vector<T>(n, value);
}
template <class... Args> auto md_vec(const usize n, Args... args) {
  return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
}
template <class T> constexpr T difference(const T &a, const T &b) {
  return a < b ? b - a : a - b;
}

} // namespace n91

#include <vector>

namespace nimi {
struct base_edge {
  std::size_t from;
  std::size_t to;
  base_edge(std::size_t from, std::size_t to) : from(from), to(to) {}
};

template <class T> struct edge : public base_edge {
  T val;
  edge(std::size_t from, std::size_t to, T v) : base_edge(from, to), val(v) {}
};

template <> struct edge<void> : public base_edge {
  edge(int from, int to) : base_edge(from, to) {}
};
template <class C> struct maxflow_edge : public base_edge {
  C cap;
  std::size_t rev;
  maxflow_edge(int from, int to, C cap, std::size_t rev)
      : base_edge(from, to), cap(cap), rev(rev) {}
};

template <class T>
struct directed_graph : public std::vector<std::vector<edge<T>>> {
  directed_graph(std::size_t n) : std::vector<std::vector<edge<T>>>(n) {}
  void add_edge(const edge<T> &e) { this->at(e.from).push_back(e); }
};

template <class T>
struct undirected_graph : public std::vector<std::vector<edge<T>>> {
  undirected_graph(std::size_t n) : std::vector<std::vector<edge<T>>>(n) {}
  void add_edge(const edge<T> &e) {
    this->at(e.from).push_back(e);
    edge<T> re = e;
    std::swap(re.from, re.to);
    this->at(e.to).push_back(re);
  }
};

template <class C>
struct maxflow_graph : public std::vector<std::vector<maxflow_edge<C>>> {
  maxflow_graph(std::size_t n) : std::vector<std::vector<maxflow_edge<C>>>(n) {}
  void add_edge(int from, int to, C cap, std::size_t rev_cap = 0) {
    this->at(from).push_back(
        maxflow_edge<C>(from, to, cap, this->at(to).size()));
    this->at(to).push_back(
        maxflow_edge<C>(to, from, rev_cap, this->at(from).size() - 1));
  }
};
} // namespace nimi

#include <limits>
#include <queue>
#include <vector>

namespace nimi {
template <class T>
std::vector<T> dijkstra(const nimi::directed_graph<T> &g, std::size_t s) {
  const T INF = std::numeric_limits<T>::max();
  const T ZERO = T();
  const std::size_t n = g.size();

  struct node {
    T dist;
    std::size_t vertex;
    node(T d, std::size_t v) : dist(d), vertex(v) {}
    bool operator<(const node &n) const { return n.dist < dist; }
  };

  std::vector<T> dist(n, INF);
  std::priority_queue<node> que;

  dist[s] = ZERO;
  que.emplace(dist[s], s);

  while (!que.empty()) {
    node p = que.top();
    T d = p.dist;
    std::size_t v = p.vertex;
    que.pop();
    if (dist[v] < d)
      continue;
    for (const auto &e : g[v]) {
      if (dist[v] + e.val < dist[e.to]) {
        dist[e.to] = dist[v] + e.val;
        que.emplace(dist[e.to], e.to);
      }
    }
  }
  return std::move(dist);
}
} // namespace nimi

#include <algorithm>
#include <array>
#include <iostream>
#include <string>
#include <utility>

namespace n91 {

void main_() {
  usize n, m;
  std::cin >> n >> m;
  nimi::directed_graph<usize> g(n * 3_z);
  for (const auto i : rep(0_z, m)) {
    usize u, v;
    std::cin >> u >> v;
    --u;
    --v;
    g.add_edge({u, n + v, 1_z});
    g.add_edge({n + u, n * 2_z + v, 1_z});
    g.add_edge({n * 2_z + u, v, 1_z});
  }
  usize s, t;
  std::cin >> s >> t;
  --s;
  --t;
  const usize dist = nimi::dijkstra(g, s)[t];
  if (dist != std::numeric_limits<usize>::max()) {
    std::cout << dist / 3_z << std::endl;
  } else {
    std::cout << "-1" << std::endl;
  }
}

} // namespace n91

int main() {
  n91::main_();
  return 0;
}


Measured memory_bytes: 18944