#include <iostream>
#include <queue>
#include <vector>
using namespace std;
const int maxn = 1e5 + 10;

vector<int> graph[maxn];
int main()
{
    int n;
    cin >> n;

    int m;
    cin >> m;

    for(int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        a--; b--;

        graph[a].push_back(b);
        graph[b].push_back(a);
    }
    int S, E;
    cin >> S >> E;
    S--;
    E--;


    queue<int> q;
    q.push(S);
    q.push(0);

    vector<bool> visited(n, false);
    while(!q.empty()) {
        int c = q.front();
        q.pop();
        int dist = q.front();
        q.pop();


        if(c == E) {
            cout << dist << endl;
            return 0;
        }
        for(int i = 0; i < (int) graph[c].size(); i++) {
            int neighbour = graph[c][i];
            if(!visited[neighbour]) {
                q.push(neighbour);
                q.push(dist + 1);
                visited[neighbour] = true;
            }

        }

    }
    cout << 0 << endl;


    return 0;

}