#include <bits/stdc++.h>
using namespace std;

using vi = vector<int>; using vvi = vector<vi>; using vvvi = vector<vvi>;
using ll = long long int;
using vll = vector<ll>; using vvll = vector<vll>; using vvvll = vector<vvll>;
using vd = vector<double>; using vvd = vector<vd>; using vvvd = vector<vvd>;
using P = pair<int, int>;
using Pll = pair<ll, ll>;
using cdouble = complex<double>;

const double eps = 1e-7;
#define Loop(i, n) for(int i = 0; i < int(n); i++)
#define Loopll(i, n) for(ll i = 0; i < ll(n); i++)
#define Loop1(i, n) for(int i = 1; i <= int(n); i++)
#define Loopll1(i, n) for(ll i = 1; i <= ll(n); i++)
#define Loopr(i, n) for(int i = int(n) - 1; i >= 0; i--)
#define Looprll(i, n) for(ll i = ll(n) - 1; i >= 0; i--)
#define Loopr1(i, n) for(int i = int(n); i >= 1; i--)
#define Looprll1(i, n) for(ll i = ll(n); i >= 1; i--)
#define Foreach(buf, container) for(auto buf : container)
#define Loopdiag(i, j, h, w, sum) for(int i = ((sum) >= (h) ? (h) - 1 : (sum)), j = (sum) - i; i >= 0 && j < (w); i--, j++)
#define Loopdiagr(i, j, h, w, sum) for(int j = ((sum) >= (w) ? (w) - 1 : (sum)), i = (sum) - j; j >= 0 && i < (h); j--, i++)
#define Loopdiagsym(i, j, h, w, gap) for (int i = ((gap) >= 0 ? (gap) : 0), j = i - (gap); i < (h) && j < (w); i++, j++)
#define Loopdiagsymr(i, j, h, w, gap) for (int i = ((gap) > (h) - (w) - 1 ? (h) - 1 : (w) - 1 + (gap)), j = i - (gap); i >= 0 && j >= 0; i--, j--)
#define Loopitr(itr, container) for(auto itr = container.begin(); itr != container.end(); itr++)
#define printv(vector) Loop(ex_i, vector.size()) { cout << vector[ex_i] << " "; } cout << endl;
#define printmx(matrix) Loop(ex_i, matrix.size()) { Loop(ex_j, matrix[ex_i].size()) { cout << matrix[ex_i][ex_j] << " "; } cout << endl; }
#define quickio() ios::sync_with_stdio(false); cin.tie(0);
#define bitmanip(m,val) static_cast<bitset<(int)m>>(val)
#define Comp(type_t) bool operator<(const type_t &another) const
#define fst first
#define snd second
#define INF INFINITY
bool feq(double x, double y) { return abs(x - y) <= eps; }
bool inrange(ll x, ll t) { return x >= 0 && x < t; }
bool inrange(vll xs, ll t) { Foreach(x, xs) if (!(x >= 0 && x < t)) return false; return true; }
int ceillog2(ll x) { int ret = 0;	x--; while (x > 0) { ret++; x >>= 1; } return ret; }
ll rndf(double x) { return (ll)(x + (x >= 0 ? 0.5 : -0.5)); }
ll floorsqrt(ll x) { ll m = (ll)sqrt((double)x); return m + (m * m <= x ? 0 : -1); }
ll ceilsqrt(ll x) { ll m = (ll)sqrt((double)x); return m + (x <= m * m ? 0 : 1); }
ll rnddiv(ll a, ll b) { return (a / b + (a % b * 2 >= b ? 1 : 0)); }
ll ceildiv(ll a, ll b) { return (a / b + (a % b == 0 ? 0 : 1)); }
ll gcd(ll m, ll n) { if (n == 0) return m; else return gcd(n, m % n); }
ll lcm(ll m, ll n) { return m * n / gcd(m, n); }

//========================================================================//

class Dijkstra {
private:
	struct node {
		int id; bool done; vi to; vll cst; int from; ll d;
	};
	struct pq_t {
		int id; ll d;
		bool operator<(const pq_t & another) const {
			return d != another.d ? d > another.d : id > another.id;
		}
	};
	vector<node> nodes;
	int n, m, source;
public:
	Dijkstra(const vvi &lst, const vvll &cst, int start) {
		n = lst.size();
		nodes.resize(n);
		Loop(i, n) nodes[i] = { i, false,{},{}, -1, LLONG_MAX };
		Loop(i, n) {
			Loop(j, lst[i].size()) {
				nodes[i].to.push_back(lst[i][j]);
				nodes[i].cst.push_back(cst[i][j]);
			}
		}
		source = start;
		nodes[source].d = 0;
		priority_queue<pq_t> pq;
		pq.push({ nodes[source].id, nodes[source].d });
		while (pq.size()) {
			int a = pq.top().id;
			pq.pop();
			if (nodes[a].done) continue;
			nodes[a].done = true;
			Loop(j, nodes[a].to.size()) {
				int b = nodes[a].to[j];
				if (nodes[b].done) continue;
				ll buf = nodes[a].d + nodes[a].cst[j];
				if (buf < nodes[b].d) {
					nodes[b].d = buf;
					nodes[b].from = a;
					pq.push({ b, nodes[b].d });
				}
			}
		}
		return;
	}
	vi get_path(int v) {
		stack<int> stk;
		stk.push(v);
		int a = v;
		while (nodes[a].from != -1) {
			stk.push(nodes[a].from);
			a = nodes[a].from;
		}
		if (a != source) return {};
		vi ret;
		while (stk.size()) {
			ret.push_back(stk.top());
			stk.pop();
		}
		return ret;
	}
	ll get_dist(int v) {
		return nodes[v].d;
	}
};

int main() {
	int n, m; cin >> n >> m;
	vvi lst(n * 3);
	vvll cst(n * 3);
	Loop(_, m) {
		int u, v; cin >> u >> v;
		u--; v--;
		Loop(k, 3) {
			lst[u * 3 + k].push_back(v * 3 + (k + 1) % 3);
			cst[u * 3 + k].push_back(1);
		}
	}
	int s, t; cin >> s >> t;
	s--; t--;
	Dijkstra dijk(lst, cst, s * 3);
	ll ans = dijk.get_dist(t * 3);
	if (ans == LLONG_MAX) {
		cout << -1 << endl;
	}
	else {
		cout << ans / 3 << endl;
	}
}

Measured memory_bytes: 72960