#include <bits/stdc++.h>  // include all standard C++ libraries

using namespace std;

// Loops
#define _overload3(_1,_2,_3,name,...) name
#define _rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(int i=int(a);i<int(b);++i)
#define _rrep(i,n) rrepi(i,n,0)
#define rrepi(i,a,b) for(int i=int(a)-1;i>=int(b);--i)

#define rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define rrep(...) _overload3(__VA_ARGS__,rrepi,_rrep,)(__VA_ARGS__)
#define each(xi, x) for (auto&& xi : x)
// Note: we can use rep(i,N) or rep(i,from,to)


// typedef
using ll = long long;
template <class T> using vec = vector<T>;
using vi   = vector<int>;
using vvi  = vector<vi>;
using vvvi = vector<vvi>;
using pii  = pair<int, int>;


// Constants

// Shorter repr for frequently used terms
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define Fi first
#define Se second


// Algorithms
#define all(x) (x).begin(), (x).end()
#define uniq(v) v.erase( unique(all(v)), v.end() )
#define perm(c) sort(all(c));for(bool c##p=1;c##p;c##p=next_permutation(all(c)))

template<class T> pair<T, size_t> max(vector<T> &x){ auto it = max_element(all(x)); return mp(*it, it-x.begin()); }
template<class T> pair<T, size_t> min(vector<T> &x){ auto it = min_element(all(x)); return mp(*it, it-x.begin()); }

template<class T> inline bool chmax(T &maxval, const T &newval) { if (maxval<newval) { maxval=newval; return 1; } return 0; }
template<class T> inline bool chmin(T &minval, const T &newval) { if (minval>newval) { minval=newval; return 1; } return 0; }

// Utilities
// Grid world utilities
int dx[4]={0,1,0,-1};
int dy[4]={1,0,-1,0};
#define inside(H,W,y,x) 0<=(x) && (x)<(W) && 0<=(y) && (y)<(H)

inline int in() {int x; cin >> x; return x;} // read int from cin
inline  ll IN() {ll x; cin >> x; return x;}  // read ll from cin



// Debug
#ifdef LOCAL
  #include "dump.hpp"
  #define debug(x) cerr << #x << ": " << x << '\n'
#else
  #define dump(...)
  #define debug(x)
#endif

// Paste snippets here!!
// Dijkstra for a weighted directed graph
//   G => adjlist
struct Dijkstra {
    typedef pair<int,int> pii;
    typedef pii Edge;  // (cost, to)
    vector<vector<Edge>> G; int V;
    Dijkstra(int V) : G(V), V(V) {}
    void add_edge(int from, int to, int cost){ G[from].push_back({cost,to}); }
    
    void solve(int from, vector<int> &d, vector<int>* back=nullptr)
    {   // back => if not nullptr, it will contain backward node id.
        fill(d.begin(), d.end(), numeric_limits<int>::max());
        priority_queue<pii, vector<pii>, greater<pii>> pq;
        if(back) back->at(from) = -1;
        d[from] = 0; pq.push({0, from});
        while(!pq.empty()){
            auto p = pq.top(); pq.pop();
            int v = p.second;
            if(d[v]<p.first) continue;
            for(int i=0;i<G[v].size();++i){
                auto &e = G[v][i]; int c = e.first;
                if(chmin(d[e.second], d[v]+c)){
                    pq.push({d[v]+c, e.second});  // new cost, node
                    if(back) back->at(e.second) = p.second;
                }
            }
        }
    }
};

// 

int main(){
  cin.tie(0); ios::sync_with_stdio(false);    // Magic for faster cin
  int n; ll m; int s, t;
  cin >> n >> m;
  vector<pii> E(m);
  rep(i,m){
    int u, v; cin >> u >> v;
    E[i] = {u-1,v-1};
  }
  cin >> s >> t;
  s--; t--;
  // 時拡張ネットワーク
  Dijkstra g(3*n);
  rep(i,m){
    int u = E[i].first;
    int v = E[i].second;
    g.add_edge(3*u, 3*v+1, 1);
    g.add_edge(3*u+1, 3*v+2, 1);
    g.add_edge(3*u+2, 3*v, 1);
  }
  vi d(3*n);
  g.solve(3*s,d);
  if(d[3*t]==numeric_limits<int>::max()) cout << -1 << endl;
  else cout << d[3*t]/3 << endl;
  return 0;
}


Measured memory_bytes: 18688