#include <vector>
#include <list>
#include <map>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <queue>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>
#include <cstdio>
#include <climits>
#include <complex>
#include <cstdint>
#include <tuple>

#define M_PI       3.14159265358979323846

using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); }
inline int readInt() { int x; scanf("%d", &x); return x; }

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;

//container util

//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define SQ(a) ((a)*(a))
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,s,n) for(int i=s;i<(int)n;++i)
#define REP(i,n) FOR(i,0,n)
#define MOD 1000000007

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define trav(a, x) for(auto& a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()


struct Edge {
    int to, cost, nm;
    Edge(int to, int cost, int nm): to(to), cost(cost), nm(nm) {}
};

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vector<Edge>> AdjList;
AdjList graph;
#define chmin(x,y) x=min(x,y)
#define chmax(x,y) x=max(x,y)
const int INF = 100000000;

ll GCD(ll a, ll b){
    if(a < b) swap(a, b);
    if(b == 0) return a;
    return GCD(b, a%b);
}

bool cmp(const pii& a, const pii& b){
    if(a.first == b.first){
        return a.second < b.second;
    }
    return a.first < b.first;
}


int N, M;
double r;
int n;
int sp, gp;
vector<vector<int>> G(100010);
int visited[100010][3];

int main() {


    //cout << fixed << setprecision(10);

    int N, M; cin >> N >> M;
    for(int i=0; i<100010; ++i){
        for(int j=0; j<3; ++j) visited[i][j]=-1;
    }
    for(int i=0; i<M; ++i){
        int u, v; cin >> u >> v;
        u--; v--;
        G[u].push_back(v);
    }

    cin >> sp >> gp;
    sp--; gp--;

    queue<pair<pair<int, int>, int>> q;
    q.push(make_pair(make_pair(sp, 0), 0));

    while(q.size()){
        pii p = q.front().first;
        int cnt = q.front().second;

        q.pop();
        int v = p.first;
        int stmt = p.second;


        if(visited[v][stmt]!=-1) continue;
        visited[v][stmt] = cnt;
        if(v == gp && stmt == 0) break;

        for(int i=0; i<G[v].size(); ++i){
            int u = G[v][i];

            if(stmt==0)
                q.push(make_pair(make_pair(u, (stmt+1)%3), cnt+1));
            else q.push(make_pair(make_pair(u, (stmt+1)%3), cnt));
        }
    }
    if(visited[gp][0] == -1){
        cout << -1 << endl;
    }else{
        cout << visited[gp][0] << endl;
    }
    return 0;
}

Measured memory_bytes: 6912