// IO
#include <cstdio>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm
#include <algorithm>
#include <cmath>
#include <numeric>

// container
#include <vector>
#include <string>
#include <tuple>
#include <set>
#include <map>
#include <unordered_map>
#include <stack>
#include <queue>
#include <deque>

// others
#include <random>
#include <limits>
#include <functional>
#include <ctime>
#include <cassert>

// type alias
using lint = long long;
using ldouble = long double;
template <class T>
using greater_priority_queue = std::priority_queue<T, std::vector<T>, std::greater<T>>;


/* ----- class ----- */

template <class Cost = int>
struct Edge {
    int src, dst;
    Cost cost;
    Edge(int src = -1, int dst = -1, Cost cost = 1)
        : src(src), dst(dst), cost(cost){};

    bool operator<(const Edge<Cost>& e) const { return this->cost < e.cost; }
    bool operator>(const Edge<Cost>& e) const { return this->cost > e.cost; }
};

template <class Cost = int>
using Edges = std::vector<Edge<Cost>>;

template <class Cost = int>
using Graph = std::vector<std::vector<Edge<Cost>>>;


/* ----- debug ----- */

#if __has_include("../setting/source/debug.hpp")
#include "../setting/source/debug.hpp"
#endif


/* ----- short functions ----- */

template <class T>
inline T sq(T a) { return a * a; }

template <class T>
inline T iceil(T n, T d) { return (n + d - 1) / d; }

template <class T>
T gcd(T a, T b) {
    while (b > 0) {
        a %= b;
        std::swap(a, b);
    }
    return a;
}

template <class T, class U>
T ipow(T b, U n) {
    T ret = 1;
    while (n > 0) {
        if (n & 1) ret *= b;
        n >>= 1;
        b *= b;
    }
    return ret;
}

// 0-indexed
template <class T, class U>
inline T kthbit(T a, U k) { return (a >> k) & 1; }

template <class T, class U>
inline T mask(T a, U k) { return a & ((1 << k) - 1); }

template <class T>
std::map<T, int> compress(std::vector<T>& v) {
    std::sort(v.begin(), v.end());
    v.erase(std::unique(v.begin(), v.end()), v.end());

    std::map<T, int> rev;
    for (int i = 0; i < v.size(); ++i) rev[v[i]] = i;
    return rev;
}

template <class T>
T Vec(T v) { return v; }

template <class T, class... Ts>
auto Vec(size_t l, Ts... ts) {
    return std::vector<decltype(Vec<T>(ts...))>(l, Vec<T>(ts...));
}


/* ----- constants ----- */

const int INF = std::numeric_limits<int>::max() / 3;
// const lint INF = std::numeric_limits<lint>::max() / 3;
// const ldouble PI = acos(-1);
// const ldouble EPS = 1e-10;
// std::mt19937 mt(int(std::time(nullptr)));


using namespace std;

constexpr int MAXV = 100010;

inline int encode(int v, int k) {
    return v + k * MAXV;
}

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

    Graph<> graph(MAXV * 3);
    for (int i = 0; i < M; ++i) {
        int u, v;
        cin >> u >> v;
        --u, --v;

        for (int j = 0; j < 3; ++j) {
            int src = encode(u, j), dst = encode(v, (j + 1) % 3);
            graph[src].emplace_back(src, dst);
        }
    }

    int S, T;
    {
        int s, t;
        cin >> s >> t;
        S = encode(--s, 0);
        T = encode(--t, 0);
    }

    vector<int> dist(MAXV * 3, INF);
    dist[S] = 0;

    queue<int> que;
    que.push(S);

    while (!que.empty()) {
        int v = que.front();
        que.pop();

        for (auto e : graph[v]) {
            if (dist[e.dst] < INF) continue;
            dist[e.dst] = dist[e.src] + 1;
            que.push(e.dst);
        }
    }

    cout << (dist[T] == INF ? -1 : dist[T] / 3) << endl;
    return 0;
}


Measured memory_bytes: 17792