// template version 1.12
using namespace std;
#include <iostream>
#include <bits/stdc++.h>

// varibable settings
#define infile "../test/sample-1.in"
#define int long long //{{{
const int INF=1e18;
const int MOD=1e9+7; //}}}

// define basic macro {{{
#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 rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define _rrep(i,n) rrepi(i,0,n)
#define rrepi(i,a,b) for(int i=(int)((b)-1);i>=(int)(a);--i)
#define rrep(...) _overload3(__VA_ARGS__,rrepi,_rrep,)(__VA_ARGS__)
#define each(i,a) for (auto&& i : a)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define pb(a) push_back(a)
#define mp(a, b) make_pair(a, b)
#define uni(x) sort(all(x));x.erase(unique(all(x)),x.end())
#define ub upper_bound
#define lb lower_bound
#define posl(A, x) (lower_bound(all(A), x)-A.begin())
#define posu(A, x) (upper_bound(all(A),x)-A.begin())
template<class T> inline void chmax(T &a, const T &b) { if((a) < (b)) (a) = (b); }
template<class T> inline void chmin(T &a, const T &b) { if((a) > (b)) (a) = (b); }

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef long double ld;
typedef pair<int,int> pii;
typedef tuple<int,int,int> iii;

template<typename T> using PQ = priority_queue<T, vector<T>, greater<T>>;
struct Fast { Fast(){ std::cin.tie(0); ios::sync_with_stdio(false); } } fast;

#if defined(PCM) || defined(LOCAL)
  #include "lib/dump.hpp"
#else
  #define dump(...) 42
  #define dump_1d(...) 42
  #define dump_2d(...) 42
#endif
//}}}

using COST = int;  // update
// using POS = tuple<int, int>;
struct POS{ 
  int node, level;
  POS(int x, int y) : node(x), level(y){};
};
bool operator<(auto &left, auto &right){
  if (left.node != right.node) return (left.node < right.node);
  else return left.level < right.level;
}

using EDGE = pair<POS, COST>;
struct GRAPH{
  map<POS, vector<EDGE>> all_edges;
  void add_edge(POS from, POS to, COST cost){
    all_edges[from].emplace_back(mp(to, cost));
  }

  auto operator[](POS pos){
    return all_edges[pos];
  }
};

map<POS, COST> dijkstra(GRAPH& G, POS start){
  map<POS, COST> d;  // 最短距離
  // TODO: vectorの場合はd[*]=INFにしておく。

  PQ<pair<COST, POS>> q;
  q.push(mp(0LL, start));
  while (!q.empty()){
    auto cp = q.top(); q.pop();
    auto cost = cp.first;
    auto pos = cp.second;

    if (d.find(pos)==d.end() || cost < d[pos]) {
      d[pos] = cost;
      for (const auto &el:G[pos]){
        auto ncost = cost + el.second;
        auto npos = el.first;
        q.push(mp(ncost, npos));
      }
    }
  }
  return d;
}

int solve(){
  int N,M;cin>>N>>M;

  GRAPH G;
  rep(m, M){
    int u,v; cin>>u>>v;
    u--;v--;

    G.add_edge(POS(u, 0), POS(v, 1), 0);
    G.add_edge(POS(u, 1), POS(v, 2), 0);
    G.add_edge(POS(u, 2), POS(v, 0), 1);
  }

  // calc min distance by G
  int s,t;cin>>s>>t;s--;t--;
  POS start=POS(s, 0);
  POS goal=POS(t, 0);
  auto d = dijkstra(G, start);

  if (d.find(goal)!=d.end()){
    cout << d[goal] << endl;
  }
  else{
    cout << -1 << endl;
  }

  return 0;
}

signed main() { //{{{
#ifdef INPUT_FROM_FILE
  std::ifstream in(infile);
  std::cin.rdbuf(in.rdbuf());
#endif
  solve();
  return 0;
} //}}}


Measured memory_bytes: 51840