#pragma GCC optimize ("O3")
#include "bits/stdc++.h"

using namespace std;
using ll = long long int;

#define debugos cout
#define debug(v) {printf("L%d %s > ",__LINE__,#v);debugos<<(v)<<endl;}
#define debugv(v) {printf("L%d %s > ",__LINE__,#v);for(auto e:(v)){debugos<<e<<" ";}debugos<<endl;}
#define debuga(m,w) {printf("L%d %s > ",__LINE__,#m);for(int x=0;x<(w);x++){debugos<<(m)[x]<<" ";}debugos<<endl;}
#define debugaa(m,h,w) {printf("L%d %s >\n",__LINE__,#m);for(int y=0;y<(h);y++){for(int x=0;x<(w);x++){debugos<<(m)[y][x]<<" ";}debugos<<endl;}}
#define all(v) (v).begin(),(v).end()
#define repeat(cnt,l) for(auto cnt=decltype(l)();(cnt)<(l);++(cnt))
#define rrepeat(cnt,l) for(auto cnt=(l)-1;0<=(cnt);--(cnt))
#define iterate(cnt,b,e) for(auto cnt=(b);(cnt)!=(e);++(cnt))
#define diterate(cnt,b,e) for(auto cnt=(b);(cnt)!=(e);--(cnt))
#define lambda(type,fun) [&]type{return(fun);}
#define assert_eq(ex,ac) if (!((ex) == (ac))) {cerr << "assertion fault(==): " #ex " = " << ex << ", " #ac << " = " << ac << endl; abort();}
const ll MD = 1000000007ll; const long double PI = 3.1415926535897932384626433832795L;
template<typename T1, typename T2> inline ostream& operator <<(ostream& o, const pair<T1, T2> p) { o << '(' << p.first << ':' << p.second << ')'; return o; }
template<typename Vec> inline ostream& _ostream_vecprint(ostream& os, const Vec& a) {
    os << '['; for (const auto& e : a) os << ' ' << e << ' '; os << ']'; return os;
}
template<typename T> inline ostream& operator<<(ostream & o, const vector<T> & v) { return _ostream_vecprint(o, v); }
template<typename T, size_t S> inline ostream& operator<<(ostream & o, const array<T, S> & v) { return _ostream_vecprint(o, v); }
template<typename T> inline T& chmax(T & to, const T & val) { return to = max(to, val); }
template<typename T> inline T& chmin(T & to, const T & val) { return to = min(to, val); }
void bye(string s, int code = 0) { cout << s << endl; exit(code); }
mt19937_64 randdev(8901016);
template<typename T, typename Random = decltype(randdev), typename enable_if<is_integral<T>::value>::type* = nullptr>
inline T rand(T l, T h, Random & rand = randdev) { return uniform_int_distribution<T>(l, h)(rand); }
template<typename T, typename Random = decltype(randdev), typename enable_if<is_floating_point<T>::value>::type* = nullptr>
inline T rand(T l, T h, Random & rand = randdev) { return uniform_real_distribution<T>(l, h)(rand); }

#if defined(_WIN32) || defined(_WIN64)
#define getc_x _getc_nolock
#define putc_x _putc_nolock
#elif defined(__GNUC__)
#define getc_x getc_unlocked
#define putc_x putc_unlocked
#else
#define getc_x getc
#define putc_x putc
#endif
#define isvisiblechar(c) (0x21<=(c)&&(c)<=0x7E)
class MaiScanner {
    FILE* fp_;
public:
    inline MaiScanner(FILE* fp) :fp_(fp) {}
    template<typename T> void input_integer(T& var) noexcept {
        var = 0; T sign = 1;
        int cc = getc_x(fp_);
        for (; cc < '0' || '9' < cc; cc = getc_x(fp_))
            if (cc == '-') sign = -1;
        for (; '0' <= cc && cc <= '9'; cc = getc_x(fp_))
            var = (var << 3) + (var << 1) + cc - '0';
        var = var * sign;
    }
    inline int c() noexcept { return getc_x(fp_); }
    inline MaiScanner& operator>>(int& var) noexcept { input_integer<int>(var); return *this; }
    inline MaiScanner& operator>>(long long& var) noexcept { input_integer<long long>(var); return *this; }
    inline MaiScanner& operator>>(string & var) {
        int cc = getc_x(fp_);
        for (; !isvisiblechar(cc); cc = getc_x(fp_));
        for (; isvisiblechar(cc); cc = getc_x(fp_))
            var.push_back(cc);
        return *this;
    }
    template<typename IT> inline void in(IT begin, IT end) { for (auto it = begin; it != end; ++it) * this >> *it; }
};
class MaiPrinter {
    FILE* fp_;
public:
    inline MaiPrinter(FILE* fp) :fp_(fp) {}
    template<typename T>
    void output_integer(T var) noexcept {
        if (var == 0) { putc_x('0', fp_); return; }
        if (var < 0)
            putc_x('-', fp_),
            var = -var;
        char stack[32]; int stack_p = 0;
        while (var)
            stack[stack_p++] = '0' + (var % 10),
            var /= 10;
        while (stack_p)
            putc_x(stack[--stack_p], fp_);
    }
    inline MaiPrinter& operator<<(char c) noexcept { putc_x(c, fp_); return *this; }
    inline MaiPrinter& operator<<(int var) noexcept { output_integer<int>(var); return *this; }
    inline MaiPrinter& operator<<(long long var) noexcept { output_integer<long long>(var); return *this; }
    inline MaiPrinter& operator<<(char* str_p) noexcept { while (*str_p) putc_x(*(str_p++), fp_); return *this; }
    inline MaiPrinter& operator<<(const string& str) {
        const char* p = str.c_str();
        const char* l = p + str.size();
        while (p < l) putc_x(*p++, fp_);
        return *this;
    }
    template<typename IT> void join(IT begin, IT end, char sep = ' ') { for (bool b = 0; begin != end; ++begin, b = 1) b ? *this << sep << *begin : *this << *begin; }
};
MaiScanner scanner(stdin);
MaiPrinter printer(stdout);class DGraph{
public:
    size_t n;
    vector<vector<int>> vertex_to;
    vector<vector<int>> vertex_from;
    
    DGraph(size_t n=1):n(n),vertex_to(n),vertex_from(n){}
    
    inline size_t size() const { return n; }
    void resize(size_t _n){ n = _n; vertex_to.resize(_n); vertex_from.resize(_n); }
    void connect(int from, int to){
        vertex_to[(size_t)from].emplace_back(to);
        vertex_from[(size_t)to].emplace_back(from);
    }
};

vector<int> dijkstraD(const DGraph& graph, int startIndex) {
    vector<int> dist(graph.size(), numeric_limits<int>::max());

    queue<pair<int, int>> que; // <dist, idx>
    que.emplace(0, startIndex);
    dist[startIndex] = 0;

    while (!que.empty()) {
        int d = que.front().first;
        int v = que.front().second;
        que.pop();
        if (dist[v] < d) continue;

        for (int u : graph.vertex_to[v])
            if (d + 1 < dist[u])
                que.emplace(dist[u] = d + 1, u);
    }
    return move(dist);
}


//

int N, M;
int S, T;
DGraph graph;

//


int main() {
    
    scanner >> N >> M;
    graph.resize(N*3);
    
    repeat(i, M) {
        int u, v;
        scanner >> u >> v;
        --u; --v;
        u *= 3; v *= 3;
        graph.connect(u, v+1);
        graph.connect(u+1, v+2);
        graph.connect(u+2, v);
       // graph.connect(u+3, v);
    }
    scanner >> S >> T;
    --S; --T;
    S = S*3; T = T*3;
    
    auto res = dijkstraD(graph, S);
    
    if (res[T] > 1e9) printer << "-1\n";
    else printer << (res[T]/3) << '\n';
    
    return 0;
}


Measured memory_bytes: 34176