#include <iostream>
#include <queue>
#include <vector>

using namespace std;

int N, M;
vector<vector<int>> graph;

int bfs(int s, int e) {
    vector<bool> visited(N + 1, false);

    queue<int> q;
    q.push(s);
    visited[s] = true;

    int distance = 0;
    while (!q.empty()) {
        int size = q.size();
        while (size--) {
            int cur = q.front();
            q.pop();

            if (cur == e) return distance;
            for (int v : graph[cur]) {
                if (!visited[v]) {
                    q.push(v);
                    visited[v] = true;
                }
            }
        }
        distance++;
    }

    return -1;
}

int main() {
    cin >> N >> M;

    graph = vector<vector<int>>(N + 1);
    for (int i = 1; i <= M; i++) {
        int a, b;
        cin >> a >> b;
        graph[a].push_back(b);
        graph[b].push_back(a);
    }

    int X, K;
    cin >> X >> K;

    int temp1 = bfs(1, K);
    int temp2 = bfs(K, X);
    if (temp1 == -1 || temp2 == -1) cout << "-1\n";
    else cout << temp1 + temp2;

    return 0;
}