#include <iostream>
#include <vector>

using namespace std;

int main() {
    long N = 0;
    long M = 0;
    cin >> N >> M;

    vector<long> tmp(N,0);
    vector<vector<long>> verges(M, tmp);

    long v1 = 0;
    long v2 = 0;
    for (long i = 0; i < M; i++) {
        cin >> v1 >> v2;
        verges[v1][v2] = 1;
        verges[v2][v1] = 1;
    }
    cin >> v1 >> v2;

    vector<bool> used (N);
    for (long i = 0; i < N; i++) {
        used[i] = false;
    }

    vector<long> dist (M);
    for (long i = 0; i < M; i++) {
        dist[i] = 400001;
    }
    dist[v1] = 0;


    long ind = v1;
    long min = 400001;
    long count = 0;
    do {
        for (long i = 0; i < N; i++) {
            if (dist[i] < min && !used[i]) {
                min = dist[i];
                ind = i;
            }
        }

        if (ind != 400001) {
            for (long i = 0; i < N; i++) {
                if (verges[ind][i] != 0) {
                    long temp = min + 1;
                    if (temp < dist[i]) {
                        dist[i] = temp;
                        count = 0;
                    }
                    if (temp == dist[i]) {
                        count++;
                    }
                }
            }
            used[ind] = true;
        }
    } while (ind != v2);

    if (min == 400001) {
        cout << -1 << endl;
    }
    else {
        cout << min << endl;
    }
    return 0;
}