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

#define NDEBUG
#include <cassert>


typedef long long ll;
typedef long double Double;
typedef unsigned long long ull;
typedef pair<int,int> ii;
typedef pair<ll,ll> llll;
typedef pair<double,double> dd;

typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<ii> vii;
typedef vector<vector<ii>> vvii;
typedef vector<ll> vll;
typedef vector<string> vs;
typedef vector<double> vd;
typedef vector<long double> vD;

#define sz(a)  int((a).size())
#define pb  push_back
#define eb  emplace_back
#define FOR(var,from,to) for(int var=(from);var<=(to);++var)
#define rep(var,n)  for(int var=0;var<(n);++var)
#define rep1(var,n)  for(int var=1;var<=(n);++var)
#define repC2(vari,varj,n)  for(int vari=0;vari<(n)-1;++vari)for(int varj=vari+1;varj<(n);++varj)
#define ALL(c)  (c).begin(),(c).end()
#define RALL(c)  (c).rbegin(),(c).rend()
#define tr(i,c)  for(auto i=(c).begin(); i!=(c).end(); ++i)
#define found(s,e)  ((s).find(e)!=(s).end())
#define mset(arr,val)  memset(arr,val,sizeof(arr))
#define mid(x,y) ((x)+((y)-(x))/2)
#define IN(x,a,b) ((a)<=(x)&&(x)<=(b))
#define cons make_pair

#define PQ(T) priority_queue<T>
#define RPQ(T) priority_queue<T,vector<T>,greater<T>>

template<class T> inline void amin(T & a, T const & b) { a = min(a, b); }
template<class T> inline void amax(T & a, T const & b) { a = max(a, b); }

inline ll square(ll x) { return x * x; }
inline ll gcd(ll a, ll b) { while(a) swap(a, b%=a); return b; }
template <typename T>
inline T mod(T a, T b) { return ((a % b) + b) % b; }


const ll MOD=1000000007LL;

ll ADD(ll x, ll y) { return (x+y) % MOD; }
ll SUB(ll x, ll y) { return (x-y+MOD) % MOD; }
ll MUL(ll x, ll y) { return x*y % MOD; }
ll POW(ll x, ll e) { ll v=1; for(; e; x=MUL(x,x), e>>=1) if (e&1) v = MUL(v,x); return v; }
ll DIV(ll x, ll y) { /*assert(y%MOD!=0);*/ return MUL(x, POW(y, MOD-2)); }



const int INF = 999999;

template <typename T>
void make_adjacent(int nV, vector<pair<ii,T>>& arcs, vector<vector<pair<int,T>>>& adj) {
	adj.resize(nV);
	for (pair<ii, T> p: arcs) {
		int u = p.first.first, v = p.first.second;
		assert(u != v);
		T distance = p.second;
		adj[u].push_back(make_pair(v, distance));
	}
}

template <typename T>
void dij1(int nV, vector<vector<pair<int,T>>>& adjacent, vector<T>& d, int start) {
	d.assign(nV, INF);
	d[start] = 0;
	vector<int> prev(nV, -1);

	priority_queue<pair<T, int>> Q;
	Q.push(make_pair(0, start));

	vector<bool> visited(nV, false);

	while (!Q.empty()) {
		T du = -Q.top().first;
		int u = Q.top().second; Q.pop();
		if (visited[u]) continue;
		visited[u] = true;

		int c = adjacent[u].size();
		for (int i=0; i<c; ++i) {
			int v = adjacent[u][i].first;
			T distance = adjacent[u][i].second;
			T alt = du + distance;
			if (d[v] > alt) {
				d[v] = alt;
				prev[v] = u;
				Q.push(make_pair(-alt, v));
			}
		}
	}
}

template <typename T>
void dij(int nV, vector<vector<pair<int,T>>>& adjacent, vector<vector<T>>& d) {
	d.resize(nV);
	for (int start=0; start<nV; ++start) {
		dij1(nV, adjacent, d[start], start);
	}
}


ll solve(int N,int M,vi& u,vi& v,int S,int T) {
    vector<pair<ii,int>> arcs;
    rep(i,M){
        rep(c,3){
            arcs.emplace_back(ii(u[i]*3+c, v[i]*3+(c+1)%3), 1);
        }
    }

    vector<vector<pair<int,int>>> adj;
    make_adjacent(N*3, arcs, adj);
	vi d(N*3);
    dij1(N*3, adj, d, S*3);
    if (d[T*3] >= INF) return -1;
    return d[T*3]/3;
}

int main() {
    int N, M; scanf("%d %d%*c", &N, &M);
    vi u(M),v(M);
    rep(i,M) {
        scanf("%d %d%*c", &u[i], &v[i]);
        u[i]--; v[i]--;
    }
    int S,T; scanf("%d %d%*c", &S, &T); --S; --T;
    cout << solve(N,M,u,v,S,T) << endl;
    return 0;
}


Measured memory_bytes: 24684