#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define SPEED ios_base::sync_with_stdio(false); cin.tie(NULL);
#define FOR(i, a, b) for (ll i = a; i < b; ++i)
#define RFOR(i, b, a) for (ll i = b; i >= a; --i)
#define ALL(x) x.begin(), x.end()
#define DEBUG(args...) { string _s = #args; replace(ALL(_s), ' ', '\0');\
replace(ALL(_s), ',', ' ');\
stringstream _ss(_s); istream_iterator<string> _it(_ss); _debug(_it, args);}
#define endl "\n"
#define F first
#define S second
#define pb(x) push_back(x)
#define mp(x, y) make_pair(x, y)

using namespace std;
using namespace __gnu_pbds;

template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

void _debug(istream_iterator<string>) {}
template<typename T, typename... Args>
void _debug(istream_iterator<string> it, T first, Args... args) {
    cerr << ">> " << *it << " : " << first << endl; _debug(++it, args...);
}
template <typename T1, typename T2>
inline ostream& operator << (ostream& out, const pair<T1, T2>& p) {
    return out << "(" << p.F << ", " << p.S << ")";
}
template<typename T>
inline ostream& operator << (ostream& out, const vector<T>& v) {
    if (v.empty()) return out << "[]";
    else { out << '['; for (auto& e : v) { out << e << ", "; } return out << "\b\b]"; }
}
template<typename T>
inline ostream& operator << (ostream& out, const set<T>& s) {
    if (s.empty()) return out << "{}";
    else { out << '{'; for (auto& e : s) { out << e << ", "; } return out << "\b\b}"; }
}
template<typename T>
inline ostream& operator << (ostream& out, const unordered_set<T>& s) {
    return out << set<T>(ALL(s));
}
template<typename T1, typename T2>
inline ostream& operator << (ostream& out, const map<T1, T2>& m) {
    if (m.empty()) return out << "{}";
    out << '{'; for (auto& p : m) { out << p << ", "; } return out << "\b\b}";
}
template<typename T1, typename T2>
inline ostream& operator << (ostream& out, const unordered_map<T1, T2>& m) {
    return out << map<T1, T2>(ALL(m));
}
template<typename T>
inline ostream& operator << (ostream& out, const ordered_set<T>& s) {
    return out << set<T>(ALL(s));
}

typedef long long ll;
typedef long double ld;
typedef vector<long long> vll;
typedef pair<ll, ll> pll;
typedef vector<pair<ll, ll>> vpll;
typedef unordered_map<ll, ll> STll;
/************************************** MAIN PROGRAM ********************************************/
const int MAX = 1e5 + 10;
vector<pair<int, int>> adj[MAX][3];
int distTo[MAX][3];
bool marked[MAX][3];
const int INF = 1e9;

void bfs(int s) {
    queue<pair<int, int>> q;
    marked[s][0] = true;
    FOR(i, 0, MAX) FOR(j, 0, 3) distTo[i][j] = INF;
    q.push({s, 0});
    distTo[s][0] = 0;
    while (!q.empty()) {
        int v, vLayer;
        tie(v, vLayer) = q.front();
        q.pop();

        for (auto p : adj[v][vLayer]) {
            int w, wLayer;
            tie(w, wLayer) = p;
            if (marked[w][wLayer]) continue;

            marked[w][wLayer] = true;
            distTo[w][wLayer] = distTo[v][vLayer] + 1;
            q.push({w, wLayer});
        }
    }
}

int main()
{
   // freopen("input.txt", "r", stdin);
    SPEED
    ll n, m;
    cin >> n >> m;
    FOR(_, 0, m)
    {
        ll u, v;
        cin >> u >> v;
        u--, v--;
        FOR(layerNo, 0, 3)
        {
            int nextLayer = (layerNo + 1) % 3;
            adj[u][layerNo].push_back({v, nextLayer});
        }
    }
    ll s, t;
    cin >> s >> t;
    s--, t--;
    bfs(s);
    cout << (distTo[t][0] == INF ? -1 : distTo[t][0] / 3);
}
/************************************** END OF PROGRAM ******************************************/
/** Stuff you should look for:
 * int overflow, array bounds, over-counting, graph is not a tree/connected
 * special cases (n=1?), set/unordered_set TLE, multi-set/set error
 * do something instead of nothing and stay organized
 */


Measured memory_bytes: 18176