#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <stack>
#include <string>
#include <vector>

const int MOD = 1e9 + 7;
const int iINF = 2147483647 / 2;
const long long int llINF = 9223372036854775807 / 2;

using namespace std;
using ll = long long int;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
using vvvl = vector<vector<vector<ll>>>;

typedef pair<ll, ll> pll;
bool paircomp(const pll &a, const pll &b) {
  if (a.first == b.first)
    return a.second < b.second;
  return a.first < b.first;
}
struct multi {
  ll first;
  ll second;
  ll third;
  multi(ll first, ll second, ll third)
      : first(first), second(second), third(third) {}
};
bool multicomp(const multi &a, const multi &b) {
  if (a.first == b.first)
    return a.second < b.second;
  return a.first < b.first;
}
#define REP(i, n) for (ll i = 0; i < (n); i++)
#define RREP(i, n) for (ll i = (n)-1; i >= 0; i--)
#define FOR(i, a, b) for (ll i = (a); i < (b); i++)
#define AUTO(i, m) for (auto &i : m)
#define ALL(a) (a).begin(), (a).end()
#define MAX(vec) *std::max_element(vec.begin(), vec.end())
#define MIN(vec) *std::min_element(vec.begin(), vec.end())
#define ARGMAX(vec)                                                            \
  std::distance(vec.begin(), std::max_element(vec.begin(), vec.end()))
#define ARGMIN(vec)                                                            \
  std::distance(vec.begin(), std::min_element(vec.begin(), vec.end()))
#define REV(T) greater<T>()
#define PQ(T) priority_queue<T, vector<T>, greater<T>>
#define VVL(a, b, c) vector<vector<ll>>(a, vector<ll>(b, c))
#define VVVL(a, b, c, d)                                                       \
  vector<vector<vector<ll>>>(a, vector<vector<ll>>(b, vector<ll>(c, d)))
#define SP(a) setprecision(a)
#define SQRT(a) sqrt((long double)(a))
#define DPOW(a, b) pow((long double)(a), (long double)(b))
#define UNIQUE(vec)                                                            \
  do {                                                                         \
    sort(ALL((vec)));                                                          \
    (vec).erase(std::unique(ALL((vec))), (vec).end());                         \
  } while (0)

ll POW(ll n, ll m) {
  if (m == 0) {
    return 1;
  } else if (m % 2 == 0) {
    ll tmp = POW(n, m / 2);
    return (tmp * tmp);
  } else {
    return (n * POW(n, m - 1));
  }
}

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
typedef ll Weight;

struct Edge {
  ll src, dst;
  Weight weight;
  Edge(ll src, ll dst, Weight weight) : src(src), dst(dst), weight(weight) {}
};
bool operator<(const Edge &e, const Edge &f) {
  return e.weight != f.weight ? e.weight > f.weight : // !!INVERSE!!
             e.src != f.src ? e.src < f.src : e.dst < f.dst;
}
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;

typedef vector<Weight> Array;
typedef vector<Array> Matrix;

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ll N, M, S, T;
  cin >> N >> M;
  vvl G(N);
  vvl G2(N);
  vl u(M), v(M);
  REP(i, M) {
    cin >> u[i] >> v[i];
    u[i]--;
    v[i]--;
    G[u[i]].push_back(v[i]);
  }
  cin >> S >> T;
  S--;
  T--;
  /*
  REP(i, N) {
    queue<ll> que1, que2, que3;
    AUTO(p, G[i]) { que1.push(p); }
    while (!que1.empty()) {
      ll q = que1.front();
      que1.pop();
      AUTO(p, G[q]) { que2.push(p); }
    }
    while (!que2.empty()) {
      ll q = que2.front();
      que2.pop();
      AUTO(p, G[q]) { que3.push(p); }
    }
    while (!que3.empty()) {
      ll q = que3.front();
      que3.pop();
      if (q != i)
        G2[i].push_back(q);
    }
  }*/

  queue<pll> que;
  que.push(make_pair(S, 0));
  vvl NG = VVL(N, 4, 0);

  while (!que.empty()) {
    pll po = que.front();
    que.pop();
    if (po.first == T && po.second % 3 == 0) {
      cout << po.second / 3 << endl;
      return 0;
    }
    if (NG[po.first][po.second % 3] == 1)
      continue;
    AUTO(p, G[po.first]) { que.push(make_pair(p, po.second + 1)); }
    NG[po.first][po.second % 3] = 1;
  }
  cout << -1 << endl;

  return 0;
}


Measured memory_bytes: 16640