/* Aa^~ kokoro ga pyonpyon suru n jaa^~
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*/

#include <bits/stdc++.h>
using namespace std;

using VI = vector<int>;
using VVI = vector<VI>;
using PII = pair<int, int>;
using LL = long long;
using VL = vector<LL>;
using VVL = vector<VL>;
using PLL = pair<LL, LL>;
using VS = vector<string>;

#define ALL(a)  begin((a)),end((a))
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define EB emplace_back
#define MP make_pair
#define MT make_tuple
#define SZ(a) int((a).size())
#define SORT(c) sort(ALL((c)))
#define RSORT(c) sort(RALL((c)))
#define UNIQ(c) (c).erase(unique(ALL((c))), end((c)))

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

#define FF first
#define SS second

template<class S, class T>
istream& operator>>(istream& is, pair<S,T>& p){
  return is >> p.FF >> p.SS;
}
template<class T>
istream& operator>>(istream& is, vector<T>& xs){
  for(auto& x: xs)
	is >> x;
  return is;
}
template<class S, class T>
ostream& operator<<(ostream& os, const pair<S,T>& p){
  return os << p.FF << " " << p.SS;
}
template<class T>
ostream& operator<<(ostream& os, const vector<T>& xs){
  for(unsigned int i=0;i<xs.size();++i)
	os << (i?" ":"") << xs[i];
  return os;
}
template<class T>
void maxi(T& x, T y){
  if(x < y) x = y;
}
template<class T>
void mini(T& x, T y){
  if(x > y) x = y;
}
void debug(istringstream&){}
template <char sep=',', class Head, class... Tail>
void debug(istringstream& iss, Head&& head, Tail&&... tail)
{
  string name;
  getline(iss, name, ',');
  cout << sep << name << "=" << head;
  debug(iss, forward<Tail>(tail)...);
}

#ifdef PYONPOI
#define DEBUG(...) \
  do{ \
    istringstream ss(#__VA_ARGS__); \
    debug<' '>(ss, __VA_ARGS__); \
    cout<<endl; \
  }while(0)
#else
#define DEBUG
#endif


const double EPS = 1e-10;
const double PI  = acos(-1.0);
const LL MOD = 1e9+7;
const int INF = 1e9;


int main(){
  cin.tie(0);
  ios_base::sync_with_stdio(false);

  int N, M;
  cin >> N >> M;

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

  VVI dist(3, VI(N, INF));
  dist[0][S] = 0;
  vector<queue<int>> q(3);
  q[0].push(S);
  bool up = true;
  while(up){
    up = false;

    REP(dd,3){
      int nd = (dd + 1) % 3;
      while(!q[dd].empty()){
        int u = q[dd].front();
        q[dd].pop();

        for(int to: G[u]){
          if(dist[nd][to] == INF){
            dist[nd][to] = dist[dd][u] + (!dd);
            q[nd].push(to);
            up = true;
          }
        }
      }
    }
  }

  int ans = dist[0][T];
  cout << (ans == INF ? -1 : ans) << endl;

  return 0;
}

Measured memory_bytes: 7296