#include <bits/stdc++.h>
using namespace std;
#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
#define fi first
#define se second
#define mp make_pair
#define itrfor(itr,A) for(auto itr = A.begin(); itr !=A.end();itr++)
template <class T> using reversed_priority_queue = priority_queue<T, vector<T>, greater<T> >;
typedef long long llong;
char moji[26]={'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
char moji2[26]={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
char moji3[10]={'0','1','2','3','4','5','6','7','8','9'};
#define Sort(a) sort(a.begin(),a.end());
#define Reverse(a) reverse(a.begin(),a.end());
#define print(a) cout << a << endl;
#define MOD llong(1e9+7)
#define MAX int(2 * 1e5 +5)
#define debug(x)  cout << #x << " = " << (x) << endl;
#define pi acos(-1.0)
#define int llong
#define INF llong(1e17)
template<class T> bool chmax(T &a,  T b) {if(a<b){a=b; return 1;} return 0;}
template<class T> bool chmin(T &a,  T b) {if(a>b){a=b; return 1;} return 0;}
bool Add(int &a,int b){a = (a + b) % MOD;}
void myprint(int* A,int A_num){
   REP(i,A_num) cout << A[i] << " ";
   cout << endl;
}



template <typename T> class Dijkstra{
    vector<pair < T, int >>* edges;
    int* par;
    T* Distance;
    int size;

public:
    Dijkstra(int n){
        size = n;
        edges = new vector<pair<T , int> >[n];
        Distance = new T[n];
        par = new int[n];
    };

    T Get_Distance(int x){
        if(x < 0 or x>= size) return T(-1);
        else return Distance[x];
    };

    void add_edge(T dist, int s,int t);

    void Disp_Graph();

    void Get_Shortest(int s);



};


template<typename T> void Dijkstra<T>::add_edge(T dist, int s,int t){
    edges[s].push_back( mp(dist, t));
}

template<typename T> void Dijkstra<T>::Disp_Graph(){
    REP(i,size){
        REP(j,edges[i].size()){
            cout << edges[i][j].se << " " << edges[i][j].fi <<endl;
        }
        cout << endl;
    }
}


template<typename T> void Dijkstra<T>::Get_Shortest(int s){
    REP(i,size) Distance[i] = T(INF);
    reversed_priority_queue< pair<T, int > > Q;
    bool used[size];
    REP(i,size) used[i] = false;
    REP(i,size) par[i] = -1;
    int Q_size = 1;
    Distance[s] = 0;
    Q.push( mp(T(0),s ) );
    while(Q_size){
        pair < T, int > x = Q.top();
        Q.pop();
        Q_size --;
        if( used[x.se]) continue;
        used[x.se] = true;
        REP(i,edges[x.se].size()){
            pair < T, int > y = edges[x.se][i];
            if(  Distance[y.se] > Distance[x.se] + y.fi){
                Distance[y.se] = Distance[x.se] + y.fi;
                Q.push( mp ( Distance[y.se],y.se) );
                Q_size ++;
                par[y.se] = x.se;
            }
        }

    }

}






signed main(){
   int n,m;
   cin >> n >> m;

   Dijkstra<int> D(3 * n);

   REP(i,m){
      int u,v;
      cin >> u >> v;
      u --;
      v --;
      D.add_edge(1,u,v + n);
      D.add_edge(1,u + n , v + 2 * n);
      D.add_edge(1, u + 2 * n , v);

   }

   int s,t;
   cin >> s >> t;
   s --;
   t --;

   D.Get_Shortest(s);
   int dist = D.Get_Distance(t);
   if(dist == INF) cout << -1 << endl;
   else cout << dist/3 << endl;

}

Measured memory_bytes: 21632