#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

#if __cplusplus >= 201103L
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
#endif

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#if __cplusplus >= 201103L
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#endif
using namespace std;

typedef long long ll;
//typedef pair<int,int> Pint;
typedef pair<ll, ll> P;
//typedef pair<int, pair<int, int>> P;
//typedef tuple<int,int,int> T;
typedef vector<ll> vec;
typedef vector<vec> mat;
#define rep(i, n) for(ll i = 0; i < n; i++)
#define revrep(i, n) for(ll i = n-1; i >= 0; i--)
ll INFL = 1LL << 60;//10^18 = 2^60
int INF = 1 << 30;//10^9
ll MOD  = 1000000007;
vector<int> dy = {0,0,1,-1};
vector<int> dx = {1,-1,0,0};
//vector<int> dy = {1, 1, 1, 0, -1, -1, -1, 0};
//vector<int> dx = {1, 0, -1, -1, -1, 0, 1, 1};

ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll pow(ll x, ll k){
  ll res = 1;
  while(k > 0){
    if(k % 2) res *= x;
    x *= x;
    k /= 2;
  }
  return res;
}

ll pow_mod(ll x, ll k){
  x %= MOD; x += MOD; x %= MOD;
  ll res = 1;
  while(k > 0){
    if(k % 2){
      res *= x; res %= MOD;
    }
    x *= x; x %= MOD;
    k /= 2;
  }
  return res;
}
ll inverse(ll x){return pow_mod(x, MOD - 2);};

ll gcd(ll a, ll b){
    if(b == 0) return a;
    return gcd(b, a % b);
}

ll N, M;
vector<ll> E[100010];
ll S, T;


ll d[100010][3];

void dijkstra(){
  priority_queue<P, vector<P>, greater<P>> pque;
  //cost, 頂点
  rep(i, 100010) rep(j, 3) d[i][j] = INFL;

  d[S][0] = 0;

  pque.push({0, S + 0 * 100010});

  while(!pque.empty()){
    ll c = pque.top().first;
    ll x = pque.top().second;
    pque.pop();
    ll e = x % 100010;
    ll di = x / 100010;
    if(d[e][di] < c) continue;

    rep(i, E[e].size()){
      ll ne = E[e][i];
      if(d[ne][(di+1)%3] > c + 1){
        d[ne][(di+1)%3] = c + 1;
        pque.push({c+1, ne + 100010 * ((di+1)%3)});
      }
    }
  }
}

int main(){
  cin >> N >> M;
  rep(i, M){
    ll u, v; cin >> u >> v;
    u--, v--;
    E[u].push_back(v);
  }
  cin >> S >> T;
  S--, T--;
  dijkstra();
  if(d[T][0] == INFL) cout << -1 << endl;
  else cout << d[T][0] / 3 << endl;
}


Measured memory_bytes: 8192