// Original C++ solution (slower):
/*

* じょえチャンネル

* 高評価・チャンネル登録よろしくおねがいします！

* https://www.youtube.com/channel/UCRXsI3FL_kvaVL9zoolBfbQ

*/



#include <bits/stdc++.h>





#define f(i,n) for(int i=0;i<(n);i++)





#define inf (int)(3e18)

#define int long long

#define mod (int)(1000000007)



#define intt long long

#define P pair<int,int>



#define rep(i,n) for(int i=0;i<n;i++)

#define REP(i,n) for(int i=1;i<=n;i++)



using namespace std;



//Library

//モッドパウ

int modpow(int x, int y, int m = mod) {

    int res = 1;

    while (y) {

        if (y % 2) {

            res *= x;

            res %= m;

        }

        x = x * x % mod;

        y /= 2;

    }

    return res;

}



int mypow(int x, int y) {

    int res = 1;

    while (y) {

        if (y % 2) {

            res *= x;

        }

        x = x * x;

        y /= 2;

    }

    return res;

}

//is the number (x) a prime number?

bool prime(int x) {

    for (int i = 2; i * i <= x; i++) {

        if (!(x % i)) {

            return false;

        }

    }

    return true;

}





//saidai-kouyakusuu

inline int gcd(int x, int y) {

    if (!y) {

        return x;

    }

    return gcd(y, x % y);

}





//number of keta

int keta(int x) {

    int ans = 0;

    while (x) {

        x /= 10;

        ans++;

    }

    return ans;

}



//sum of keta

int ketasum(int x) {

    int ans = 0;

    while (x) {

        ans += x % 10;

        x /= 10;

    }

    return ans;

}



inline int lcm(int x, int y) {

    int ans = x / gcd(x, y) * y;

    return ans;

}



int twobeki(int x) {

    int ans = 0;

    while (1) {

        if (!(x & 1)) {

            ans++;

            x /= 2;

        }

        else {

            break;

        }

    }

    return ans;

}





template <class T, class U>

inline bool chmax(T& lhs, const U& rhs) {

    if (lhs < rhs) {

        lhs = rhs;

        return 1;

    }

    return 0;

}

template <class T, class U>

inline bool chmin(T& lhs, const U& rhs) {

    if (lhs > rhs) {

        lhs = rhs;

        return 1;

    }

    return 0;

}

void Yes(){

    cout<<"Yes"<<endl;

}

void No(){

    cout<<"No"<<endl;

}

void YES(){

    cout<<"YES"<<endl;

}

void NO(){

    cout<<"NO"<<endl;

}



class modInt {

    int value, modulo;

public:

    modInt() : value(0), modulo(mod) { value = 0; }

    template<typename T>

    modInt(T value = 0, int modulo = mod) : value(value), modulo(modulo) {

        if (value < 0) {

            value = -value;

            value %= modulo;

            value = -value;

            value += modulo;

        }

        this->value = value % modulo;

    }

    inline operator int()const { return value; }

    inline modInt& operator+=(modInt x) {

        value += x.value;

        if (value >= modulo)value -= modulo;

        return *this;

    }

    inline modInt& operator++() {

        if (value == modulo - 1)value = 0;

        else value++;

        return *this;

    }

    inline modInt& operator-()const {

        return modInt(0) -= *this;

    }

    inline modInt& operator-=(modInt x) {

        value -= x.value;

        if (value < 0)value += modulo;

        return *this;

    }

    inline modInt& operator--() {

        if (value == 0)value = modulo - 1;

        else value--;

        return *this;

    }

    inline modInt& operator*=(modInt x) {

        value = value * x.value % modulo;

        return *this;

    }

    inline modInt& operator/=(modInt x) {

        return operator*=(x.inv());

    }

    inline modInt inv() {

        return modpow(*this, modulo - 2);

    }

    template<typename T> modInt operator+(T x) { return modInt(*this) += x; }

    template<typename T> modInt& operator+=(T x) { return operator+=(modInt(x, modulo)); }

    template<typename T> modInt operator-(T x) { return modInt(*this) -= x; }

    template<typename T> modInt& operator-=(T x) { return operator-=(modInt(x, modulo)); }

    template<typename T> modInt operator*(T x) { return modInt(*this) *= x; }

    template<typename T> modInt& operator*=(T x) { return operator*=(modInt(x, modulo)); }

    template<typename T> modInt operator/(T x) { return modInt(*this) /= x; }

    template<typename T> modInt& operator/=(T x) { return operator/=(modInt(x, modulo)); }

};

istream& operator>>(istream& ist, modInt& x) {

    int a;

    ist >> a;

    x = a;

    return ist;

}



#define fin(i) scanf("%lld",&i)

#define fout(i) printf("%lld",i)

#define fendl printf("\n")

//Library-End





int n,m,u,v,s,t,kyo[300004];

bool went[300004];

vector<int> road[300004];





signed main() {

    cin>>n>>m;

    

    rep(i,m){

        fin(u);fin(v);

        road[u*3].push_back(v*3+1);

        road[u*3+1].push_back(v*3+2);

        road[u*3+2].push_back(v*3);

    }

    

    cin>>s>>t;

    queue<int> q;

    q.push(s*3);

    while (!q.empty()) {

        int x=q.front();

        q.pop();

        went[x] = true;

        for (int i = 0; i < (int)road[x].size(); i++) {

            if (!went[road[x][i]]) {

                went[road[x][i]]=1;

                q.push(road[x][i]);

                kyo[road[x][i]]=kyo[x]+1;

            }

        }

    }

    if(went[t*3])cout<<kyo[t*3]/3<<endl;

    else cout<<-1<<endl;

}








// Optimized solution to the same problem (faster):
/*

 * じょえチャンネル

 * 高評価・チャンネル登録よろしくおねがいします！

 * https://www.youtube.com/channel/UCRXsI3FL_kvaVL9zoolBfbQ

 */



#include <bits/stdc++.h>



//#pragma GCC target("avx2")

//#pragma GCC optimize("O3")

//#pragma GCC optimize("unroll-loops")









//here!!!

// define int long long !!!!!



#define int long long



// define int long long !!!!!





#define mod (int)((1e9)+7)

//constexpr int mod = 998244353ll;





#ifdef int

#define inf (int)(3e18)

#else

#define inf (int)(5e8)

#endif



#define intt long long

#define itn long long

#define P pair<long long,long long>



#define rep(i,n) for(int i=0;i<n;i++)

#define REP(i,n) for(int i=1;i<=n;i++)

#define rev_rep(i,n) for(int i=n-1;i>=0;i--)

#define REV_REP(i,n) for(int i=n;i>=1;i--)



#define ALL(v) v.begin(),v.end()



#define smallpriority_queue(x) priority_queue<x,vector<x>,greater<x>>



using namespace std;



//Library

//モッドパウ

inline int modpow(int x, int y, int m = mod) {

    int res = 1;

    while (y) {

        if (y & 1) {

            res *= x;

            res %= m;

        }

        x = x * x % m;

        y /= 2;

    }

    return res;

}



int mypow(int x, int y) {

    int res = 1;

    while (y) {

        if (y % 2) {

            res *= x;

        }

        x = x * x;

        y /= 2;

    }

    return res;

}

//is the number (x) a prime number?

bool prime(int x) {

    if (!x || x == 1) {

        return false;

    }

    for (int i = 2; i * i <= x; i++) {

        if (!(x % i)) {

            return false;

        }

    }

    return true;

}





//saidai-kouyakusuu

inline int gcd(int x, int y) {

    if (!y) {

        return x;

    }

    return gcd(y, x % y);

}





//number of keta

int keta(int x) {

    int ans = 0;

    while (x) {

        x /= 10;

        ans++;

    }

    return ans;

}



//sum of keta

int ketasum(int x) {

    int ans = 0;

    while (x) {

        ans += x % 10;

        x /= 10;

    }

    return ans;

}



inline int lcm(int x, int y) {

    int ans = x / gcd(x, y) * y;

    return ans;

}

int twobeki(int x) {

    int ans = 0;

    while (1) {

        if (!(x & 1)) {

            ans++;

            x >>= 1;

        }

        else {

            break;

        }

    }

    return ans;

}





template <class T, class U>

inline bool chmax(T& lhs, const U& rhs) {

    if (lhs < rhs) {

        lhs = rhs;

        return 1;

    }

    return 0;

}

template <class T, class U>

inline bool chmin(T& lhs, const U& rhs) {

    if (lhs > rhs) {

        lhs = rhs;

        return 1;

    }

    return 0;

}

void Yes(){

    cout<<"Yes"<<endl;

}

void No(){

    cout<<"No"<<endl;

}

void YES(){

    cout<<"YES"<<endl;

}

void NO(){

    cout<<"NO"<<endl;

}





#define fin(i) scanf("%lld",&i)

#define fout(i) printf("%lld",i)

#define fendl printf("\n")



int kai(int x, int y) {

    int res = 1;

    for (int i = x - y + 1; i <= x; i++) {

        res *= i; res %= mod;

    }

    return res;

}



int comb(int x, int y) {

    if (y > x)return 0;

    //    cout<<kai(x, y)<<' '<<modpow(kai(y, y), mod - 2)<<endl;

    return kai(x, y) * modpow(kai(y, y), mod - 2) % mod;

}

//Library-End





#define vecin(v) for(int i=0;i<v.size();i++)scanf("%lld",&v[i]);

#define vecout(v) {for(int i=0;i<(int)v.size();i++)printf("%lld ",v[i]);printf("\n");}





template<typename T>

class kaageSegTree {

protected:

    unsigned int n = 1, rank = 0;

    std::vector<T> node;

    T nodee;

    virtual T nodef(const T&, const T&)const = 0;

public:

    kaageSegTree(unsigned int m, T init, T nodee):nodee(nodee) {

        while (n < m) {

            n *= 2;

            rank++;

        }

        node.resize(2 * n);

        for (unsigned int i = n; i < 2 * n; i++)node[i] = init;

    }

    kaageSegTree(const std::vector<T>& initvec, T nodee):nodee(nodee) {

        unsigned int m = initvec.size();

        while (n < m) {

            n *= 2;

            rank++;

        }

        node.resize(2 * n);

        for (unsigned int i = n; i < 2 * n; i++) {

            if (i - n < m)node[i] = initvec[i - n];

        }

    }

    virtual void update(int i, T x) {

        i += n;

        node[i] = x;

        while (i != 1) {

            i >>= 1;

            node[i] = nodef(node[2 * i], node[2 * i + 1]);

        }

    }

    virtual T query(int l, int r) {

        l += n; r += n;

        T ls = nodee, rs = nodee;

        while (l < r) {

            if (l & 1) {

                ls = nodef(ls, node[l]);

                l++;

            }

            if (r & 1) {

                r--;

                rs = nodef(node[r], rs);

            }

            l >>= 1; r >>= 1;

        }

        return nodef(ls, rs);

    }

    virtual T operator[](const int& x) {

        return node[n + x];

    }

    void fill(T x) {

        std::fill(ALL(node), x);

    }

    void print() {

        rep(i, n)std::cout << operator[](i) << " ";

        std::cout << std::endl;

    }

};

class RSQ :public kaageSegTree<int> {

    int nodef(const int& lhs,const int& rhs)const{return lhs+rhs;}

public:

    RSQ(int size, const int& def = 0) :kaageSegTree<int>(size, def, 0) {}

    RSQ(const std::vector<int>& initvec) :kaageSegTree<int>(initvec, 0) {}

};

class RMiQ :public kaageSegTree<int> {

    int nodef(const int& lhs,const int& rhs)const{return std::min(lhs,rhs);}

public:

    RMiQ(int size, const int& def = 0) :kaageSegTree<int>(size, def, inf) {}

    RMiQ(const std::vector<int>& initvec) :kaageSegTree<int>(initvec, inf) {}

};

class RMaQ :public kaageSegTree<int> {

    int nodef(const int& lhs,const int& rhs)const{return std::max(lhs,rhs);}

public:

    RMaQ(int size, const int& def = 0) :kaageSegTree<int>(size, def, -inf) {}

    RMaQ(const std::vector<int>& initvec) :kaageSegTree<int>(initvec, -inf) {}

};

template<typename T, typename U>

class IntervalSegTree :public kaageSegTree<T> {

protected:

    using kaageSegTree<T>::n;

    using kaageSegTree<T>::rank;

    using kaageSegTree<T>::node;

    using kaageSegTree<T>::nodef;

    using kaageSegTree<T>::nodee;

    std::vector<U> lazy;

    std::vector<bool> lazyflag;

    std::vector<int> width;

    virtual void lazyf(U&, const U&) = 0;

    virtual void updf(T&, const U&, const unsigned int&) = 0;

    void eval(int k) {

        for (int i = rank; i > 0; i--) {

            int nk = k >> i;

            if (lazyflag[nk]) {

                updf(node[2 * nk], lazy[nk], width[2 * nk]);

                updf(node[2 * nk + 1], lazy[nk], width[2 * nk + 1]);

                if (lazyflag[2 * nk])lazyf(lazy[2 * nk], lazy[nk]);

                else lazy[2 * nk] = lazy[nk];

                if (lazyflag[2 * nk + 1])lazyf(lazy[2 * nk + 1], lazy[nk]);

                else lazy[2 * nk + 1] = lazy[nk];

                lazyflag[2 * nk] = lazyflag[2 * nk + 1] = true;

                lazyflag[nk] = false;

            }

        }

    }

public:

    IntervalSegTree(unsigned int m, T init, T nodee) :kaageSegTree<T>(m, init, nodee) {

        lazy.resize(2 * n); lazyflag.resize(2 * n); width.resize(2 * n);

        width[1] = n;

        for (unsigned int i = 2; i < 2 * n; i++) {

            width[i] = width[i >> 1] >> 1;

        }

    }

    IntervalSegTree(T nodee, const std::vector<T>& initvec) :kaageSegTree<T>(initvec, nodee) {

        lazy.resize(2 * n); lazyflag.resize(2 * n); width.resize(2 * n);

        width[1] = n;

        for (unsigned int i = 2; i < 2 * n; i++) {

            width[i] = width[i >> 1] >> 1;

        }

    }

    void update(int i, U x) {

        i += n;

        eval(i);

        updf(node[i], x, width[i]);

        if (lazyflag[i])lazyf(lazy[i], x);

        else {

            lazyflag[i] = true;

            lazy[i] = x;

        }

        while (i /= 2)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

    void update(int l, int r, U x) {

        l += n; r += n;

        int nl = l, nr = r;

        while (!(nl & 1))nl >>= 1;

        while (!(nr & 1))nr >>= 1;

        nr--;

        eval(nl); eval(nr);

        while (l < r) {

            if (l & 1) {

                updf(node[l], x, width[l]);

                if (lazyflag[l])lazyf(lazy[l], x);

                else {

                    lazyflag[l] = true;

                    lazy[l] = x;

                }

                l++;

            }

            if (r & 1) {

                r--;

                updf(node[r], x, width[r]);

                if (lazyflag[r])lazyf(lazy[r], x);

                else {

                    lazyflag[r] = true;

                    lazy[r] = x;

                }

            }

            l >>= 1; r >>= 1;

        }

        while (nl >>= 1)node[nl] = nodef(node[2 * nl], node[2 * nl + 1]);

        while (nr >>= 1)node[nr] = nodef(node[2 * nr], node[2 * nr + 1]);

    }

    T query(int l, int r) {

        l += n; r += n;

        eval(l); eval(r - 1);

        int ls = nodee, rs = nodee;

        while (l < r) {

            if (l & 1) {

                ls = nodef(ls, node[l]);

                l++;

            }

            if (r & 1) {

                r--;

                rs = nodef(node[r], rs);

            }

            l >>= 1; r >>= 1;

        }

        return nodef(ls, rs);

    }

    T operator[](const int& x) {

        eval(n + x);

        return node[n + x];

    }

    T queryForAll() {

        return node[1];

    }

};

class RAQRSQ :public IntervalSegTree<int, int> {

    int nodef(const int& a, const int& b)const { return a + b; }

    void lazyf(int& a, const int& b) { a += b; }

    void updf(int& a, const int& b, const unsigned int& width) { a += width * b; }

public:

    RAQRSQ(int size, const int& def = 0) :IntervalSegTree<int, int>(size, def, 0) {

        for (int i = n - 1; i > 0; i--)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

    RAQRSQ(const std::vector<int>& initvec) :IntervalSegTree<int, int>((int)0, initvec) {

        for (int i = n - 1; i > 0; i--)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

};

class RAQRMiQ :public IntervalSegTree<int, int> {

    int nodef(const int& a, const int& b)const { return std::min(a, b); }

    void lazyf(int& a, const int& b) { a += b; }

    void updf(int& a, const int& b, const unsigned int& width) { a += b; }

public:

    RAQRMiQ(int size, const int& def = 0) :IntervalSegTree<int, int>(size, def, inf) {

        for (int i = n - 1; i > 0; i--)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

    RAQRMiQ(const std::vector<int>& initvec) :IntervalSegTree<int, int>(inf, initvec) {

        for (int i = n - 1; i > 0; i--)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

};

class RAQRMaQ :public IntervalSegTree<int, int> {

    int nodef(const int& a, const int& b)const { return std::max(a, b); }

    void lazyf(int& a, const int& b) { a += b; }

    void updf(int& a, const int& b, const unsigned int& width) { a += b; }

public:

    RAQRMaQ(unsigned int size, const int& def = 0) :IntervalSegTree<int, int>(size, def, -inf) {

        for (int i = n - 1; i > 0; i--)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

    RAQRMaQ(const std::vector<int>& initvec) :IntervalSegTree<int, int>(-inf, initvec) {

        for (int i = n - 1; i > 0; i--)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

};

class RUQRSQ :public IntervalSegTree<int, int> {

    int nodef(const int& a, const int& b)const { return a + b; }

    void lazyf(int& a, const int& b) { a = b; }

    void updf(int& a, const int& b, const unsigned int& width) { a = width * b; }

public:

    RUQRSQ(int size, const int& def = 0) :IntervalSegTree<int, int>(size, def, 0) {

        for (int i = n - 1; i > 0; i--)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

    RUQRSQ(const std::vector<int>& initvec) :IntervalSegTree<int, int>((int)0, initvec) {

        for (int i = n - 1; i > 0; i--)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

};

class RUQRMiQ :public IntervalSegTree<int, int> {

    int nodef(const int& a, const int& b)const { return std::min(a, b); }

    void lazyf(int& a, const int& b) { a = b; }

    void updf(int& a, const int& b, const unsigned int& width) { a = b; }

public:

    RUQRMiQ(int size, const int& def = 0) :IntervalSegTree<int, int>(size, def, inf) {

        for (int i = n - 1; i > 0; i--)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

    RUQRMiQ(const std::vector<int>& initvec) :IntervalSegTree<int, int>(inf, initvec) {

        for (int i = n - 1; i > 0; i--)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

};

class RUQRMaQ :public IntervalSegTree<int, int> {

    int nodef(const int& a, const int& b)const { return std::max(a, b); }

    void lazyf(int& a, const int& b) { a = b; }

    void updf(int& a, const int& b, const unsigned int& width) { a = b; }

public:

    RUQRMaQ(int size, const int& def = 0) :IntervalSegTree<int, int>(size, def, -inf) {

        for (int i = n - 1; i > 0; i--)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

    RUQRMaQ(const std::vector<int>& initvec) :IntervalSegTree<int, int>(-inf, initvec) {

        for (int i = n - 1; i > 0; i--)node[i] = nodef(node[2 * i], node[2 * i + 1]);

    }

};



////SegTree

//template <class T>

//class SegTree {

//    int n;                       // 葉の数

//    vector<T> node;              // データを格納するvector

//    T def;                       // 初期値かつ単位元

//    function<T(T, T)> operation; // 区間クエリで使う処理

//    function<T(T, T)> update;    // 点更新で使う処理

//

//    // 区間[a,b)の総和。ノードk=[l,r)に着目している。

//    T _query(int a, int b, int k, int l, int r) {

//        if (r <= a || b <= l) return def; // 交差しない

//        if (a <= l && r <= b)

//            return node[k]; // a,l,r,bの順で完全に含まれる

//        else {

//            T c1 = _query(a, b, 2 * k + 1, l, (l + r) / 2); // 左の子

//            T c2 = _query(a, b, 2 * k + 2, (l + r) / 2, r); // 右の子

//            return operation(c1, c2);

//        }

//    }

//

//public:

//    // _n:必要サイズ, _def:初期値かつ単位元, _operation:クエリ関数,

//    // _update:更新関数

//    SegTree(size_t _n, T _def, function<T(T, T)> _operation,

//            function<T(T, T)> _update)

//    : def(_def), operation(_operation), update(_update) {

//        n = 1;

//        while (n < _n) {

//            n *= 2;

//        }

//        node = vector<T>(2 * n , def);

//    }

//

//    // 場所i(0-indexed)の値をxで更新

//    void change(int i, T x) {

//        i += n - 1;

//        node[i] = update(node[i], x);

//        while (i > 0) {

//            i = (i - 1) / 2;

//            node[i] = operation(node[i * 2 + 1], node[i * 2 + 2]);

//        }

//    }

//

//    // [a, b)の区間クエリを実行

//    T query(int a, int b) {

//        return _query(a, b, 0, 0, n);

//    }

//

//    // 添字でアクセス

//    T operator[](int i) {

//        return node[i + n - 1];

//    }

//};



template <class T>

class SegTree {

    int n;

    vector<T> node;

    T def;

    function<T(T,T)> operation;

    function<T(T,T)> update;

    

public:

    SegTree(unsigned int _n, T _def, function<T(T, T)> _operation,

            function<T(T, T)> _update)

    : def(_def), operation(_operation), update(_update) {

        n=1;

        while (n < _n) {

            n *= 2;

        }

        node = vector<T>(n * 2, def);

    }

    SegTree(vector<int>& initvec, function<T(T, T)> _operation,

            function<T(T, T)> _update)

    :  operation(_operation), update(_update) {

        n=1;

        while (n < initvec.size()) {

            n *= 2;

        }

        node = vector<T>(n * 2, def);

        for(int i=n;i<n+initvec.size();i++){

            node[i]=initvec[i-n];

        }

        for(int i=n-1;i>=1;i--){

            node[i]=operation(node[i*2],node[i*2+1]);

        }

    }

    void change(int i,T x){

        i+=n;

        node[i]=update(node[i],x);

        while (i>=1) {

            i>>=1;

            node[i]=operation(node[i*2],node[i*2+1]);

        }

    }

    T query(int l, int r){

        l+=n;

        r+=n;

        T rx=def,lx=def;

        while(l<r){

            if (l&1) {

                lx=operation(lx,node[l]);

                l++;

            }

            if (r&1) {

                r--;

                rx=operation(node[r],rx);

            }

            l>>=1; r>>=1;

        }

        return operation(lx,rx);

    }

    T operator [] (const int& x){

        return node[x-n];

    }

    void fill(T x) {

        std::fill(ALL(node), x);

    }

    void print() {

        rep(i, n)std::cout << operator[](i) << " ";

        std::cout << std::endl;

    }

    

};



#define R_MIN ([](long long a, long long b) { return min(a, b); })

#define R_MAX ([](long long a, long long b) { return max(a, b); })

#define R_SUM ([](long long a, long long b) { return a + b; })



#define NORMAL_UPDATE ([](long long a, long long b) { return b; })

#define ADD_UPDATE ([](long long a, long long b) { return a + b; })

#define MINUS_UPDATE ([](long long a, long long b) { return a - b; }



class Union_Find {

    vector<int> par;

    vector<int> rankmy;

    vector<int> ookisa;

    

public:

    Union_Find(int size) {

        par = vector<int>(size);

        rankmy = vector<int>(size);

        ookisa=vector<int>(size);

        for (int i = 0; i < size; i++) {

            par[i] = i;

            ookisa[i]=1;

        }

    }

    

    int find(int x) {

        if (par[x] == x) {

            return x;

        }

        return par[x] = find(par[x]);

    }

    

    void unite(int x, int y) {

        x = find(x);

        y = find(y);

        if (x == y) {

            return;

        }

        if (rankmy[x] < rankmy[y]) {

            par[x] = y;

            ookisa[y]+=ookisa[x];

            ookisa[x]=0;

        }

        else {

            par[y] = x;

            ookisa[x]+=ookisa[y];

            ookisa[y]=0;

            if (rankmy[x] == rankmy[y]) {

                rankmy[x]++;

            }

        }

    }

    int size(int i){

        i=find(i);

        return ookisa[i];

    }

    bool same(int x, int y){

        return find(x) == find(y);

    }

    

};



class BIT {

    vector<int> data;

    int size=0;

public:

    BIT(int _size){

        data=vector<int>(_size+1);

        size=_size;

    }

    void add(int i,int x){

        while (i<=size) {

            data[i]+=x;

            i += i & -i;

        }

    }

    int sum(int i){

        assert(i<=size);

        int s=0;

        while(i>0){

            s+=data[i];

            i -= i & -i;

        }

        return s;

    }

    int lower_bound(int x){

        if(x<=0){

            return 0;

        }else{

            int i=0;int r=1;

            while(r<size) r=r<<1;

            for(int len=r;len>0;len=len>>1) {

                if(i+len<size && data[i+len]<x){

                    x-=data[i+len];

                    i+=len;

                }

            }

            return i+1;

        }

    }

};



//Union-Find-End



int perm[2000005];

void init_perm() {

    perm[0] = 1;

    REP(i, 2000004) {

        perm[i] = perm[i - 1] * i % mod;

    }

}



int nCk(int x, int y) {

    if (x<0) {

        return 1;

    }

    if (y>x) {

        return 0;

    }

    return perm[x] * modpow(perm[x - y], mod - 2) % mod * modpow(perm[y], mod - 2) % mod;

}



double kyori(pair<int, int> f, pair<int, int> s) {

    double ans = 0;

    double t = fabs(f.first - s.first);

    double y = fabs(f.second - s.second);

    ans = sqrt(t * t + y * y);

    return ans;

}



inline string stringmax(string& x,string& y){

    if (x.size()>y.size()) {

        return x;

    }

    if (x.size()<y.size()) {

        return y;

    }

    rep(i,x.size()){

        if (x[i]>y[i]) {

            return x;

        }

        if (x[i]<y[i]) {

            return y;

        }

    }

    return x;

}



vector<int>  RollingHash(string &s, string& t){

    vector<int> ans;

    __int128 h=0,hamod=0,ki=0,kim=0,hikaku=0,one=0;

    one=1;

    ki=1000000007ll;

    hamod=(one<<61)-1;

    kim=1;

    rep(i,t.size()){

        hikaku*=ki;

        h*=ki;

        kim*=ki;

        hikaku+=t[i];

        h+=s[i];

        hikaku%=hamod;

        h%=hamod;

        kim%=hamod;

    }

    rep(i,(int)s.size()-(int)t.size()+1){

        if (h==hikaku) {

            ans.emplace_back(i);

        }

        h*=ki;

        h%=hamod;

        h+=s[i+(int)t.size()];

        h%=hamod;

        h+=hamod;

        h-=s[i]*kim%hamod;

        h%=hamod;

    }

    return ans;

}

struct edge {

    int to;

    int length;

    edge(int _to, int _length){

        to=_to;

        length=_length;

    }

};

vector<int> djkstra(vector<vector<edge>> &road,int start){

    vector<int> kyo(road.size(),inf);

    smallpriority_queue(P) q;

    q.push({0,start});

    kyo[start]=0;

    while (q.size()) {

        int x=q.top().second;

        itn now=q.top().first;

        q.pop();

        if (kyo[x]<now) {

            continue;

        }

        for(auto&i:road[x]){

            if (kyo[i.to]>now+i.length) {

                kyo[i.to]=now+i.length;

                q.push({kyo[i.to],i.to});

            }

        }

    }

    return kyo;

}



#define endl "\n" //interactive の時に注意！！！

#define printd cout<<fixed<<setprecision(10)





int n,m,u[100004],v[100004],s,t,ans;

vector<int> kyo;

signed main() {

    ios::sync_with_stdio(false);

    std::cin.tie(nullptr);

    cin>>n>>m;

    vector<vector<edge>> road(n*3+5);

    rep(i,m){

        cin>>u[i]>>v[i];

        road[u[i]*3].push_back(edge(v[i]*3+1, 1));

        road[u[i]*3+1].push_back(edge(v[i]*3+2, 1));

        road[u[i]*3+2].push_back(edge(v[i]*3, 1));

    }

    cin>>s>>t;

    kyo=djkstra(road, s*3);

    if (kyo[t*3]!=inf) {

        cout<<kyo[t*3]/3<<endl;

    }else{

        cout<<-1<<endl;

    }

}














// Fastest known solution for this problem: