#pragma GCC optimize("Ofast")
#include<bits/stdc++.h>
using namespace::std;
//struct __INIT{__INIT(){cin.tie(0);ios::sync_with_stdio(false);cout<<fixed<<setprecision(15);}} __init;
__attribute__((constructor))
void init(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(15);
}
// random_device rd;
// mt19937 mt(rd());
// #include <boost/numeric/interval.hpp>
// #include <boost/numeric/interval/io.hpp>
// #include <boost/intrusive/rbtree.hpp>
// #include <boost/dynamic_bitset.hpp>
// #include <boost/geometry.hpp>
// #include <boost/geometry/geometries/linestring.hpp>
// #include <boost/geometry/geometries/polygon.hpp>
// #include <boost/geometry/geometries/point_xy.hpp>
// #include <boost/math/tools/minima.hpp>
// using boost::math::tools::brent_find_minima;
// #include <boost/multiprecision/cpp_dec_float.hpp>
// #include <boost/multiprecision/cpp_int.hpp>
// namespace mp = boost::multiprecision;
// typedef mp::number<mp::cpp_dec_float<256>> cdouble;
// typedef mp::cpp_int cint;

#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/priority_queue.hpp>
#include<ext/pb_ds/tag_and_trait.hpp>
template<typename T=long long>using pbds=__gnu_pbds::tree<T,__gnu_pbds::null_type,less<T>,__gnu_pbds::rb_tree_tag,__gnu_pbds::tree_order_statistics_node_update>;
template<typename T=long long>using pbds_map=__gnu_pbds::tree<T,T,less<T>,__gnu_pbds::rb_tree_tag,__gnu_pbds::tree_order_statistics_node_update>;
template<typename T=long long>using pqueue =__gnu_pbds::priority_queue<T, less<T>,__gnu_pbds::rc_binomial_heap_tag>;
typedef long long lint;
typedef long long ll;
typedef long double ldouble;
typedef vector<lint> vec;
typedef vector<vector<lint>> mat;
typedef vector<vector<vector<lint>>> mat3;
typedef vector<double> dvec;
typedef vector<vector<double>> dmat;
typedef vector<vector<vector<double>>> dmat3;
typedef vector<string> svec;
typedef vector<vector<string>> smat;
typedef vector<vector<vector<string>>> smat3;
typedef vector<pair<lint,lint>> pvec;
typedef vector<vector<pair<lint,lint>>> pmat;
typedef vector<vector<vector<pair<lint,lint>>>> pmat3;
#define rep(i, n) for(lint i = 0; i < (lint)(n); i++)
#define irep(i) for(lint i = 0;; i++)
#define irep1(i) for(lint i = 1;; i++)
#define irep2(i) for(lint i = 2;; i++)
#define rrep(i, n) for(lint i = (lint)(n-1); i >-1; i--)
#define rrepi(i,a,b) for(lint i = (lint)(b-1); i >a-1; i--)
#define repi(i,a,b) for(lint i=lint(a);i<lint(b);i++)
#define rep2(i,a,b,c) for(lint i=lint(a);i>lint(b);i+=c)
#define all(x) (x).begin(),(x).end()
#define PI 3.141592653589793
#define dist(x1,y1,x2,y2) (pow(pow(x2-x1,2)+pow(y2-y1,2),0.5))
#define input(a,n) lint n;cin>>n;vector<lint>a(n);rep(i,n)cin>>a[i];
#define SUM(v) accumulate(all(v),0LL)
#define INF (1LL<<60)
#define IINF (1<<30)
#define EPS (1e-10)
#define LINF 9223372036854775807
//#define MOD 998244353LL
#define MOD 1000000007LL
#define endl "\n"
template<typename T>inline void numout(T t){bool f=0;for(auto i:t){cout<<(f?"":" ")<<i<INF/2?i:"INF";f=1;}}
template<typename T>inline void numout2(T t){for(auto i:t)numout(i);cout<<endl;}
template<typename T>inline void output(T t){bool f=0;for(auto i:t){cout<<(f?"":" ")<<i;f=1;}}
template<typename T>inline void output2(T t){for(auto i:t)output(i);cout<<endl;}
template<typename T>inline void _output(T t){bool f=0;for(int i=0;i<t.size();i++){cout<<f?"":" "<<t[i];f=1;}}
template<typename T>inline void _output2(T t){for(int i=0;i<t.size();i++)output(t[i]);cout<<endl;}
auto Y=[&](auto f){return[&](auto... args){return f(f, args...);};};
template<typename T=lint>T in(){return *istream_iterator<T>(cin);}
template<typename T=lint>inline T gcd(T a,T b){return b?gcd(b,a%b):a;}
template<typename T=lint>inline T lcm(T a,T b){return a/gcd(a,b)*b;}
template<typename T=lint>inline T minq(T a,T b){return min(a,b);}
inline bool chmin(auto& s,const auto& t){bool res=s>t;s=min(s,t);return res;}
inline bool chmax(auto& s,const auto& t){bool res=s<t;s=max(s,t);return res;}
vector<int> dx={-1,1,0,0,1,1,-1,-1};
vector<int> dy={0,0,-1,1,1,-1,1,-1};

template<typename T>
inline void compress(vector<T>& t,vector<T>& s){
	s=t;
	sort(all(s));
	s.erase(unique(all(s)),s.end());
	rep(i,t.size())t[i]=lower_bound(all(s),t[i])-s.begin();
}

//comp(a,b) means a<b
template<typename Weight,typename Diff,typename Add,typename Comp,typename Int>
vector<Weight> dij(const vector<vector<pair<Int,Diff>>>&v,const Int& s,const Weight& zero,const Weight& inf,const Comp& comp,const Add& add){
    Int n=v.size();
    vector<Weight> ans(vector<Weight>(n,inf));
    ans[s]=zero;
    using pq_t=__gnu_pbds::priority_queue<pair<Weight,Int>,function<bool(pair<Weight,Int>,pair<Weight,Int>)>,__gnu_pbds::pairing_heap_tag>;
    pq_t que([&comp](auto s,auto t){return comp(t.first,s.first);});
    typename pq_t::point_iterator node[n];
    for(Int i=0;i<n;i++)node[i]=que.push(make_pair(inf,i));
    que.modify(node[s],make_pair(zero,s));
    while(!que.empty()){
        Weight p;
        Int now;
        tie(p,now)=que.top();
        que.pop();
        for(auto d:v[now]){
            auto next=add(p,d.second);
            if(comp(next,ans[d.first])){
				ans[d.first]=next;
				que.modify(node[d.first],make_pair(next,d.first));
			}
        }
    }
	return ans;
}

int main(){
	lint n,m;
    cin>>n>>m;
    pmat v(n*3);
    rep(i,m){
        lint a,b;
        cin>>a>>b;
        a--;b--;
        rep(k,3){
            v[a*3+k].emplace_back(b*3+(k+1)%3,1);
        }
    }
    lint s,t;
    cin>>s>>t;
    s--;t--;
    auto ans=dij(v,s*3,0LL,INF,[](auto s,auto t){return s<t;},[](auto s,auto t){return s+t;});
    if(ans[t*3]>INF/2)cout<<-1<<endl;
    else cout<<ans[t*3]/3<<endl;
}

Measured memory_bytes: 35456